OP asked them to stop, they didn't. They took enjoyment in aggravating the OP. They earned that split lip.

Next time they decide to deliberately provoke someone, perhaps they'll consider this event first.

There's a wonderful little exchange in Mr. Inbetween, where he's in anger management and they're asking him why he beat up some asshole teenagers:

They were being assholes.

Well sure... but the world's full of assholes.

Yea, you know why? Because we let them.

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Problems don't get fixed until we start to deal with them. This is how you deal with assholes.