How do you know if a guy is flirting with you?

I'm asking because there have been more than once this year where my cousin has tolled me that me and my guy friend were flirting with each other and I didn't believe her. I don't know when a guy is flirting with me or not and this also includes texting I don't know.

I would like to know because then I will hope fully be able to ask them not to.

How do you know if a guy is flirting with you?
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