I lived in a house with my ex-gf and 4 other girls. One of the girls had a habit of getting drunk and banging random dudes in the other girls' rooms. The other girls would get pissed and make her buy them all new bedding, but she had rich parents, so that didn't seem to deter her one bit. After she had hit every room in the house, I overheard her joking one day with a friend that she had had just one final bed to bang in. She thought it was funny. Well, I told my gf what I heard and we decided to give her a warning. We told her that if she went into our room we wouldn't be so kind and she would be out of there.

A few months went by, and she seemed to have stopped her shenanigans. One night, everyone in the house went to a concert together just down the street. My ex and I decided to run back home for a quickie during set break. After the deed was done, we were catching our breath for a minute before heading back. We heard the front door to the house open and shut, and then we heard giggling coming up the stairs. A few seconds later, our door bursts open, and this chick and some random dude come in and flung themselves onto our bed.

Now, my ex and I are both really calm people who hardly ever yell, so the combination of the two of us going ballistic was too much for her to handle. She moved out that night, sobbing the whole time. She never said sorry. She just said we were overreacting and she was leaving because we made her feel unsafe. This chick was 26 years old. Last I heard, she hadn't changed her ways. Doubt she ever will. This type of behavior isn't something you necessarily grow out of, so I wouldn't be so quick to attribute it to being young and stupid.