What is the funniest insult / joke you've come up with on the spot?
For me it was "Your mom looks like Gimli from Lord of the Rings.". My best friend took a few seconds to process what I just said to him and then started crying laughing. Good times. I think it was the deadpan delivery that killed him.
In highschool I was in shop class with some idiots that were messing around with a running table saw. The teacher saw the obvious kick back danger and swooped down on them with an angry "Hay! Do you want to have kids?!". Before I could stop myself I said "Damn, you should at least buy them dinner first."
He was not amused, but I am still proud of the one time in my life I was quick witted enough to come up with something funny on the spot. It's been so years 30 years since, and nothing has come close.
My buddy had gotten a job in a posh part of town. He told me that one of the unexpected benefits was that every woman he saw was dressed to impress with perfect hair, makeup, and clothing.
"Joe, you gotta get over this sick fetish you have for women who bathe every day."
A young woman I knew was complaining that she had made plans to meet a friend in the city (long before most people had mobile phones), but the friend hadn't showed up so she waited for a long time on the street corner.
My brother immediately chipped in, "what was his name, John?"
Saturday before Easter... 17 or 18 year old kid was going on and on about how he couldn't wait to get home so he could play Call of Duty all night, and this and that... lots of swearing, lots of talk about shooting and destruction.
Me: "I dunno man, don't you have to be in bed early so the Easter Bunny will come?"
Not me, but a friend. She got insulted by a drunk female nazi who happened to be... Ugly as fuck,not only because her ideology.
Very calm and mannered she simply told her:"Excuse me, Ma'am, as I midwife I feel professional inclined to forward an important piece of advice to your dear mother: Usually you throw the afterbirth away and keep the baby,not vice versa. "