It's one of those things that works in movies because it's something you can get away with if you're incredibly attractive. There's a whole stock images category involving girls licking their fingers, mostly in a seductive style. But, in the real world, it's something you do with your husband or long-term partner, not a random cow-orker.
But those girls are licking their OWN food off their fingers, not pasta sauce from sticking their hand into a co-worker's spaghetti! Even within an intimate relationship grabbing the other person's food isn't appropriate without consent.
Siblings doing something to your food isn't a sign it's appropriate, more the opposite. We're worst behaved towards each other, although we'd defend them against others.
LOL my partner is a germaphobe and would be very upset if I touched his food. I'll cook it, sure, but I sure as fuck wouldn't poke his food with my bare hands randomly at dinner.
It wasn’t flirting, but this ADHD positive girl I was crushing on(and was crushing on me) once absentmindedly stuck the tip of her finger in a full glass of water in front of her to ask whose it was and I had to desperately fight falling in love right then and there.
Now, that was an accident born of silly brain vs purposefully fucking with someone’s food so I understand the difference, but I really like my story so…