What is the most disrespectful thing anyone has ever done to you?

i'm a junior in high school, and this girl who i have trouble dealing with is a freshman (sabrina). she's been so rude and disrespectful ALL year, and we have one class together. when i'm up on stage acting, she has the nerves to throws insults at me and my performance when she can't even memorize a single line herself. whenever i approach her (like in a casual manner), she goes off at me with an attitude. and a couple of weeks ago, our class was in the auditorium. sabrina was sitting behind me. and soon after i hung my jacket up on my seat, she decided to place her feet on it (as if it was some resting spot). after waiting 20 minutes in aggravated silence, i turned around and kindly asked her to get her feet off my jacket. she refused. i asked her again, and she repeatedly refused. her boyfriend told me that i could just put my jacket on the seat next to me, and sabrina started telling me the same thing. i got so aggravated with her and her attitude, i gave her the finger. and she was like, "yeah, that's normal." she didn't dare take her feet off my jacket, not even once, and i had to YANK my jacket out from under her feet. i wanted to hit her, but at the same, i didn't want to cause a scene. she only does this to me (because to her, being a ***** to an upperclassman makes her look cool). and this girl doesn't even know me, and i don't know her.