I had a sexual assault once in high school. It's kind of like what MysticSang'ha described happening to her, but I didn't handle it as efficiently at the time.
I was at lunch, sitting at a table on the outer perimeter of the cafeteria with friends. This guy sat with us that day, who was loosely acquainted with one of the boys at our table, and he just kind of made himself at home at the table. He was a senior, older than me, and very suave and handsome and all that, and he started making people laugh and stuff, so we thought he was cool.
After a few minutes, he started turning his sights towards me, flirting, which I didn't mind at first. He went to the vending machine, and then came back and sat next to me rather than in the chair he was at before, and started to really directly flirt. Like, he brushed his fingers through my hair, complemented me a ton, said I smelled nice, just started making loose contact to break the touch barrier, and then he tickled my side, and I was beginning to feel uncomfortable but was still kind of playing along with it because at the time I felt that I didn't want to make a scene. I did tell him to stop but I purposely made it not sound serious.
But then, he quickly put his hand right on my lower abdomen, under my top, with his finger tips right at the edge of my jeans. I put my hand on his wrist to try to push it away, still without making a scene, and I didn't think he would ever do what he ended up doing. People at the table were laughing because they thought he was tickling me again, since they could see his arm over toward me but the table was blocking the view. Before I could react, he did what I didn't think he'd do, and quickly reached his hand down under my jeans and underwear between the legs, purposely stopping just short of directly touching my private area. I grabbed his wrist to pull his hand out but he was using strength to keep it in, moving his finger around right above that area, which was still a very sensitive spot to be touching, especially when not consensual. After a few seconds (table friends thought I was being tickled, freaking out), I got away from him and slid toward the other end of the table.
At that point I should have left and gone to the principle or something, but I was in some kind of shock where I just didn't want to move, didn't want anyone to look at me, and still didn't want to make a scene. My friends saw that something was wrong, nobody was sure what, and the bell was about to ring at any moment. There was like an awkward minute where I was pretending to focus on eating the remainder of my food while other people, including the guy, were doing kind of the same thing. In my head I was preparing myself to knock the wind out of him if he moved near me. The bell rang and I got out of there, he found me in the hallway and was like, "You know I was just kidding right? I didn't mean anything, just playing around." but I just got away from him, didn't want to talk to him, didn't want him near me.
I never had any contact with him after that. It was running through my head a lot that day as I replayed the scene in my head, feeling foolish for letting him violate my space inch by inch. I was annoyed at how it happened, how he flirted, got positive feedback, flirted more directly and started violating my personal space, and then the next second he's literally in the pants.
By the next day I was back to normal, and mostly forgot about it.