Angry or amused?

Either ignore or an eye roll.

I would just fail to notice it, I have found that seemingly being unaware when someone is trying to shock by either making gestures or saying something that is meant to be shocking, rather takes the wind out of their sails.

They hope to shock us old fogeys. Best to show that all they are is boring.

I have no idea what you mean but I can guess.
Poor deprived souls, they can't be living very interesting lives if that sort of thing amuses them.

I suspect I'd laugh.

Best thing is ignoring them as most have said because the airheads are only waiting for a reaction and when that's not forthcoming they'll just go on to the next one, or give up altogether. Let's hope the next one gives them a fourpenny one !

I would have ignored them, but sometimes a reciprocal gesture has a shock effect.
My ex father in law, who thought a woman's place was barefoot and pregnant in the kitchen, was always giving women drivers a mouthful of foul abuse, until the day a smartly dressed woman in an expensive car simply stared expressionlessly at him then gave him a V sign and drove away.
He was speechless.

I’d have ignored them.

Ignored them, they thought they would anger or embarrass

" so" engrossed not saw!

I used to work as a car valeter, we had the massive windows car show room windows.

A young lad (prob start of secondary school used to walk past making gestures

But one day he was saw engrossed making the gestures he forgot about the Lampost!!! ha ha ha lol Oh !! revenge as they say is best served cold lol. "Smack" right into the lampost. lol 40 yrs later I can still picture the scene lol

I remember a child doing that at school! Last day of term and handing out ice lollies to the class, and a particularly obnoxious child started doing it to his lolly. Luckily he was seen by another teacher who whipped the lolly out of his hands, so he went without. Serve him right, I'm afraid.

I like to be tucked up safely indoors when the school kids are about.

Ignored them.

I'd probably go back to reading my paper whilst I slowly gave them the middle finger.

Having never seen that gesture ( I live a sheltered life)
Not sure how obscene it was, but think I would have shook my head pityingly at them and gone back to reading the paper.

Definitely ignore. Turn your back and find something interesting in the cafe. I blame the parents

Just what you did, they hate being ignored.