Assholes don't care about any feelings but their own, assholes don't think about anyone but themselves when they're making a decision, and assholes will put you down every chance they get - whether they realize it or not.
I had a friend who was an unintentional* asshole in high school, and I told her the truth many times before it got through to her. I felt I owed it to her, because she was my best friend, we had an unexplained connection, etc. V. good friend of mine. When I told her, she was sorry, and cleaned up her act for a while. But after behaving for a little while, she started up with the same sort of behaviour, and that's when I cut the cord. I didn't have any contact with her for more than 2 years.
*I have to believe it was unintentional.
Recently, about two years ago, she called my house. She hung up. Now, we don't have caller ID at my parent's house, and I hadn't talked to her in more than two years, but I just knew it was her. (We apparently still have that unexplained connection.) I looked in at my mom in the next room, said, "They hung up, but... I think it was Jackie!" She called back a few seconds later and we talked for a while. I was v. cold to her at first (self-preservation, don't ya know), but eventually agreed that we could meet up and get some drinks. I wanted to give her another chance, I guess.
Though the course of the night, it became completely clear that she was just the same as she'd always been, and I spent most of the time at the bar talking another aquaintance that happened to be there. I don't regret it at all, however. It gave me peace of mind to let her have her say. I think everyone deserves a second chance.