Well... There was the recent roommate. Was my best friend for ten years, I took care of him, stuck my life on the line for him, defended him through everything, and I could swear he'd do the same for me.
Then he became my roommate and promptly stabbed me in the back. He still to this day owes me $1100 I covered for him because he decided he didn't have to pay his bills and I did, and turned his back on me and tried to shut me out of his life because I (supposedly) slandered him to his girlfriend of two months after they got engaged. I told her she was making a mistake in the engagement. That's it. Top that off with the fact that he was lying to his father (a very good friend of mine) about me and trying to turn him against me, and I'm feeling pretty unforgiving at this point.