Flirting

Guys, How do I respond to playful punches?

So there's this guy I like and we are kinda friends and will hang out with a group sometimes. And sometimes instead of talking he will playfully punch my arm or tap my face, and I have replied with the whole "you wanna fight?" And some playful punches back, but it feels weird. Is there a different way to respond? Does he expect me to do something different?
Guys, How do I respond to playful punches?
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