"Can i ask you for a favor?" Is it rude to say no?

"You can ask."

That's a pretty good answer. Indicates you're not taking any bullshit without being rude.
A good answer

I don't think it's rude. It's a favor, after all, not expected behavior.

I almost always respond with, "depends on the favor." They could be asking for you to take their picture; they could be asking for $1000 for their MLM. I'm not signing a blank check by answering "yes".

This is my go-to as well, never fails. Because a lot of the things people want me to do for them (especially at work in public-facing job) are legitimately things I won’t or don’t want to do.

As some others have said, no, it's not rude to decline. Whether or not it's rude is in how you word it. You were rude in this particular instance.

On the contrary, it'd be rude to expect any other answer. Shoving expectations onto a complete stranger and then judging them for firmly denying you is what's rude here.
The question is rude in this context. It's not rude to completely ignore rude questions.

Your rationalization sounds like some self centered manipulative bullying bullshit.

you are not obligated to speak to a random person in public at all

Congrats, you just dodged a fae bargain.

'No.' is a complete sentence and you do not have to justify yourself in any way. I don't think that would be considered rude, either.

"Sorry, I can't help you." Why? Because sometimes I hand out random favors, but not today to you.

Why? Because I can't, like I said.

No one has to justify themselves. You asked, I said no. The end.

"You can ask."

Well, yes, I would say it's rude if you have no reason to say no. At least hear them out is usually considered nice.

But...

If the person is clearly wanting to sell something to me, or trick me into something, or take advantage of me (typical in touristic places) I would just say "no thanks" and move on.

Not at all everyone has their own set of boundaries and if you don't want to do something for a stranger that's OK too.

Thanks, that's kind of my stance. I'm suspicious of random humans.

Assume they're asking because they want to make sure it's not imposing, in which case it's good to assert boundaries you need too. If they push it was just a manipulation tactic, in which case you're more than justified in walking.

He walked away. Said something about it's not for money or something, I'm very suspicious of random humans.

Since he walked away i assume he meant no harm. I thought it strange shrug.
- Sometimes people use that question rhetorically because it feels polite, viewing it as a small talk precursor to ease in to actually just saying what they want.
  
  I don't like when people use it as such, because it is insincere, poor consent practice, and low-key manipulative due to the foot in the door phenomenon .
  
  There are tons of legitimate reasons to not be comfortable with the question. Don't have time, bad headspace, don't feel comfortable... If they can't understand that, I try not to care what they think of me.
- There's beggers all around in my area. I say no all the time. You get tired of all the same begging bs very quickly.
  
  At least he didn't continue asking you and following you.

When I was growing up, attending Jewish day school, my Rabbi taught me that an opportunity to help a stranger is a gift. I would entertain the question and I recommend that you do too in the future. Obviously you don't need to comply with any unreasonable requests but typically a stranger is only going to ask you for something that takes like 2 minutes of your time and no real loss.

Helping people is enriching and will give you a sense of well-being in this fucked up grim world. You come out ahead in these situations. On the flip side, it's clear that refusing this stranger is eating at you at least a little and has done some tiny damage to your soul, strictly figuratively speaking.

I take your point, and in general agree with it. We should try to help.

Hoever, someone approaches like that and my radar is going off. Sorry, my safety comes first, so I'm just going to say "No thanks", every time, because we all know this person is trying to scam someone. (And I literally mean "No thanks" - It's oddly disarming by reversing the roles, if only for a moment).

Someone once told me "don't let them use your principles against you", which is exactly what this scammer is doing.

There's a world of difference between helping a stranger and allowing yourself to be pulled into a potentially risky situation.

This is the same reason I never pick up hitch hikers (I have in certain areas/circumstances).

Though I have no problem helping someone on the side of the road. I've helped random people carry stuff out of the store to their car - by offering to help them.

These are different situations which you can assess in the moment.
- I should add... I also take self defense very seriously, I lived in a town with active neonazis for a good portion of my adult life (outside of my control)
  
  My willingness to engage with strangers is backed up by street smarts, heavy emphasis on situational awareness, and a disarming personality. I also keep pepper spray in my hand in my coat pocket at all times and I carry a handgun.
  
  IMO nobody should let low scam resistance and physical vulnerability stop them from engaging with strangers if they have the ability to properly mitigate these risks. Wise up, get training, become exceptionally dangerous so you have the choice to be exceptionally kind.
  
  If weapons are offputting to you due to cultural or political reasons, get fit and allow yourself to sprint the other direction if you feel threatened. This is the best way to win 90% of self defense encounters anyways.

Rudeness is in the presentation, not the fact.

If you say "fuck off", that's rude.

If you say "I don't do favors for people I don't know" or "I don't take requests from strangers" those are neutral and acceptable facts.

If you say "you can ask, but it doesn't mean I'll do it" that's another neutral and acceptable way to address it if you're willing to see what the favor might be, since some favors might me acceptable.

I tend to be willing to hear the request, but only with the caveat that I will most likely not comply. Last time a stranger asked if I could "help them", my response was "I doubt I can, and I might not, but ask away". They asked, and all they wanted was a light. I no longer smoke, but I carry a lighter. So I checked the surroundings and lit his cig

Years ago, I had a patient that lived in a really shifty area, and folks would approach me on my way up to their apartment. I'd see them coming and before they could reach me, I'd tell them that if they were wanting something to not waste their time, but if they were looking for trouble, they found it.

Which was rude in other circumstances, but necessary in that place at that time.

Your response was acceptable in that time at that place. Not necessarily the friendliest way of phrasing it, but sometimes being friendly doesn't go well.

The ones that you call neutral, I would say are still rude.
- There's always leeway in that kind of thing for sure.
  
  Part of it Is what we assume is the minimum degree of energy/effort we're required to spend on a given person. Places with a higher degree of obligation to strangers are going to see what I call neutral as anything from rude to outright antisocial.
  
  Even here in the south, where the obligation is relatively minor, my neutral would be seen as unfriendly, though not rude. People shit on southern hospitality because it can seem artificial, but there is a genuine "code" where the standard of obligation is higher than in many places in the US. Someone approaches you politely in public here, you really are supposed to hear them out at least. Some of the older folks still think that if someone drops by to visit you almost have to invite them in if they're even remotely known to you. And likely offer them a drink. And you won't talk shit about them until they leave lol.
firmly agree. It's all about the presentation. For example, using what was provided above the act of just saying no was a neutral sentence. Adding afterward that that's just sus changed it from being a neutral to a negative because now you're accusing the other person of being sketchy/sus,without providing the ability to prove otherwise. That I find rude.

I think I agree with most of the replies here saying that the way it was handled was rude. If the opening response to me talking to someone was like that, I would feel like, okay, who pissed in your cheerios and I would have walked off.

Like others have said, there's more to the solution than a yes or no. I personally think "depends on the favor" , is a very appropriate response, or a "maybe what do you want" Or if you're planning on saying no regardless, do it how you did, without calling the other person creepy, its just extremly rude to assume someone is a creep while also shutting them down before they can actually talk.

No

my usual answer when I'm suspecting some kind of boundary-pushing behavior is "well you can ask..." ...but I have to hear out my psych patients, you don't owe strangers the same obligation.

I'd say something like "uhhh what's up?" or "maybe?" and let them ask a specific question since saying yes sort of feels like agreeing to do the favor without knowing what it is first.

It's not rude at all IMO. Some people like to help some others not, simply as that.

I tend to say something along the lines of "what's your problem?"

Gives an opening to hear more without committing, and makes it clear it's still THEIR problem.

"I'm sorry but I really don't have the bandwidth right now."

You do not owe any random person anything.

(yes really. It may be rude on occasion but you do not owe politeness to just anyone either. And oftentimes politeness is also abused)

He was probably going to ask you to take a photo or something. It’s fine to say no, but kind of rude to refuse to hear the request.

I don't care if I'm rude to someone who's trying to scam me, or in this case started being inconsiderate themselves.

Stephen Covey discusses this in Seven Habits of Highly Successful People. He's asked if it's OK to lie to someone. He answers by posing a scenario where being honest gets you killed, but using a harmless lie you aren't.

I highly recommend reading the book.

Bit rude, yeah, but sometimes it's better to be rude than let someone cross your boundaries. How much more awkward is it if you say "yes" or "maybe" and then they ask if they can borrow your phone or something and you have to evaluate whether you trust this random person while they're looking right at you? A lot of people are definitely asking this way because it gets you to let your guard down and they know you would've said no if they'd just straight asked. Personally I tend to respond with "you can ask" or something like that. Making it pretty clear that I'm skeptical of what they're going to ask. But my default assumption of other people in a city is that they're potentially either trying to scam me or rob me.

A lot of people are saying similar.
- It also sounds like they targeted you specifically while you were waiting in line. So not only did they only approach you about it when they could've asked anybody, they approached you in a place where it's hard for you to just walk away. That's sus to me, I think your instincts were right to not give them an in.

Not gonna lie, I was here to call you an asshole for not even hearing out the request, then I read it was a random dude on the street. Nah, refusing to engage with strangers on the street in any capacity is not rude and, depending on where you live, it may be a smart thing to do.

No, but people often sees you like the guy who doesn't do any favors

I was taught to say "Depends on the favor" but was also told that's rude...but by someone who wanted a favor so maybe we can discount that opinion.

No, perfectly fine. Shuts down a needles discussion that you don't want to have early.

More broadly, I think it's appropriate to respond to social overreaching with rudeness.

In situations like these, I tend to just not respond but simply look at them. Awkward for everyone, but not aggressive on my part. Leave the ball in their court, if it's a simple "could you take a photo" then whatever, but if it's a less acceptable "could you buy me some smokes" then you've not mentally committed.