Friend keeps taunting me about my ?

My friend Mel ruthlessly taunts me about my s. I have of larger size..so I'm kind of used to be talked to about it, but this is too much. Whenever she comes over to my house she hits, punches, and kicks my s. Then she laughs and says "Well they are so big you probably can't feel it anyways!" I tell her to stop and she won't listen. Once time i was painting in a tank top and she took a paint brush and splattered paint all over my and then pushed me off my chair. What should I do?