My best friend had a pretty bad one:
We were at a festival, having fun, drinking beer, smoking weed (Netherlands, it's legal, you federal agencies!). My best friend's girlfriend had a bit too much of the sauce and proceeded to get very friendly with everyone at our campsite on the camping ground, including me. I wasn't having any of it though, contrary to two other good friends of ours who were stoned and drunk out of their minds. She kissed both of them right in front of my best friend's face, then proceeded to tell my best friend she just wanted to be friends.
He was broken for the rest of the day. I felt terrible for him. His entire day at the festival-and his relationship of course- was completely ruined. One of the few he was able to keep going for a little while.
Luckily afterwards we both agreed that the ruined festival day was the worst of the two.