How do you respond to flirting?

I'm not very good at responding to flirting. I don't know how to take a compliment other than "thank you," and I don't really know anything witty to say in return.

There's this guy who is just flirty by nature. I know for a fact that he's not interested in me (asked him), and he flirts with lots of girls. After I asked him if he liked me he backed off for a while but he's started to flirt again and I never know how to respond. (Today he wolf-whistled because I curled my hair nicely.)

How can I respond to him? What kind of phrases do you use to be flirty?
How do you respond to flirting?
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