See, I had a friend similar to that a couple months ago. He and I were best friends since 7th grade, but the summer break after our senior year in high school, he just absolutely went to shit.

Now, I don't ever talk to him or see him any more (partly because he goes to college so far away, and partly because I can't stand the fucker).

My advice would be, if you can bear it, to just drop his ass. I admit, it was hard for me at first because we had been such good friends for so long and I didn't want to throw it all away but after sitting on it for a while and coming to terms with it, I'm glad I did. Because now I don't have to put up with his superioristic, know-it-all attitude.