Late to the party, but here it is nonetheless:
Backgoround: My best friend was a girl, and we were both high schoolers, meaning that hormones and peer pressure already put undue strain on the friendship even once we ourselves had decided where we stood (just friends, nothing more). She had a not-so-great childhood to put it mildly and sometimes the stress and such would be too much and she'd lash out at people around her. I'm typically very laid back, so for the most part this wasn't a big deal, but my patience isn't infinite either and at times it got trying.
The actual event in question started our senior year when she got a new boyfriend. The week prior we had hung out every single day after school, but once they started dating she stopped so much as texting me outside of classes. That was annoying, but not the end of the world. After a couple of weeks of this she started hanging out with another mutual friend - who she frequently invited to my place when we had plans, without checking with me - but never once was I invited to hang out with the two of them. After something like 4-5 weeks since she started dating this guy she finally was willing to hang out with me again, but for a long time only with our other mutual friend too. I was really upset with her for how she treated me, but tried to let it go and continued on as if nothing was wrong.
We hung out a few more times, but I was still super annoyed with her for how she handled the situation, so when not too much later she invited myself and a few mutual friends over for a literal pity party because the BF broke up with her I was pissed about it. Again I tried to get past it and cool off, but the final straw was some two weeks later when she called me and invited me to hang out because our friend was having a mini-party, just a bunch of friends getting together. She told me she'd call me back once she knew what time it was starting. She never called me back and I was so angry I just said "Well, I'm never initiating a conversation with her again, let's see what happens." Yeah, still waiting on that phone call to this day.