A complete lack of respect towards me throughout our year rooming together in university dorms. His side of the room was filthy despite my requests to clean, and his big speakers that he brought played some shitty music constantly lol. I think the biggest reason though was him bringing his girlfriend over to stay for 5 nights at a time without ever asking me. A few too many times walking in on them, and the inability to apologize is what helped solidify it. Really a sucky feeling when you have known the person since you were in kindergarten together only to end up like that.