There used to be a guy I'd regularly see whenever I held my sister's parties. He was reasonably nice if you talked to him but majority of the time he would be the quieter one who just drank and never really got involved too much. I used to talk to him because I had seen him looking at me a few times and thought he wanted to talk or something.
No idea what gave him the impression I liked him but he would actually start to follow me around. He even showed up at the house of some guy I had been sleeping with at the time. I didn't notice until it got pointed out to me on the quiet. Then before Christmas last year, he groped my boob and tried to kiss me.
I was actually terrified because he was about 6'4 and much heavier than I was. One of my sister's friends ended up catching him and dealt with him later on. Haven't seen the guy since but I can't say I miss him.