Girls, Is this her way of flirting or is she just an a*s hole?

I really like my friend she is so pretty and fun to be around and she is a tomboy so she does all the things I like to do except she does this thing where she sack taps (she flicks the back of her hand or fist into my nuts suddenly) me in public to embarrass me. She does it while I'm ordering food or in front of my mom and sister or even in front of our teacher. Is this some way of flirting or is she just an a*s hole and hurting me like that to embarrass me? And how can I get her to stop doing it?
Girls, Is this her way of flirting or is she just an a*s hole?
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