Hands to yourself DAMNIT

Ok, so I am at a local burger place (Red Robin). So I am sitting there minding my own business when someone grabs my ass. Ok so I am sitting, how can someone grab my ass while I am sitting you may ask. Just before the ass grab I felt something hit my back and fall between the chair and my back. So I am thinking she dropped something and reached for it and just bumped my butt. Ok sounds good to me, but no it happens two more times. So please tell me what the hell is up with that. I feel so violated.