I've had some of the biggest douchebags for friends in my life, so here it goes.
When I was a sophmore in high school, I was dating a guy who also happened to be a close friend of mine. We weren't exclusive so maybe it's not so bad, but my friends did know how I felt. Friend #1 started dating him simultaneously. Friend #2 hung out with him when I was away and hooked up with him in her basement. Friend #3 began a sexual relationship with him a few weeks after prom.
So I figured, whatever, they're just not good friends, and stopped hanging out with all four of them and became closer with my other friends (most of which I'd known for 6-10 years at that point).
We went camping over the summer for a long weekend for one of their birthdays. Halfway through, the one girl lost around $50 somehow. We searched the entire area and all of the beds and stuff, never found out. They never outright accused me of anything, but started acting so badly towards me I actually called my mom and left because I was miserable.
When I got home, one of our friends who had been in vermont and hadn't gone along told me "I was the most likely culprit because I didn't have a job". So that makes me a scumbag? Riiight.
For whatever reason, I let this slide, and senior year rolled around. It was nearing the time to pick roommates for the senior trip to disney world, and we had always had it set to be myself and my two friends I had known the longest, plus the one girls best friend.
But the day we got the sign up sheets in homeroom, my "best" friend of nearly 11 years now was sitting next to me filling out the paperwork. The girl sitting near her asked "who are you rooming with" and she replied "I don't know". I knew it was bad, but glanced over her shoulder and saw my name replaced with their new friend. They didn't even have the decency to tell me so I could find other roommates, and I ended up not going at all.
Needless to say, I hate most people my age. All of my current friends are in their early to mid 30s (I'm turning just 21 next month). It might seem weird to some people, but at least I don't have to deal with the ridiculous garbage that consumed me during high school.