Ones that I can remember -
1) Gay dude on my Facebook keeps on throwing his sexuality in people's faces, promotes his photography work just because he has an expensive camera, can use Photoshop, and has HELPED photograph a wedding. Have told him to his face about his making a point about his sexuality, albeit in a kinda offensive way, which made him cry. Someone did tell him once when he was claiming stress that it was stressful for everyone working with him. Needless to say, I had to like that comment.
2) Girl I used to be best friends with tweeting about how she hates cheaters, despite the fact that she cheated on her boyfriend about a year and a half ago and was only staying with him because she didn't want to be lonely. I would have said something, but she's friends with my girlfriend, so my balls would have been ripped off.
3) My ex turned lesbian about 3 years after we broke up, her and her girlfriend (at the time) would have public arguments and displays of affection over Facebook. The former I actually commented on to try and diffuse the situation, attempting to help my ex; was told to go fuck myself by BOTH OF THEM. The latter - many of us thought the messages were cringeworthy and should have been saved for in private, and somebody made a point about it and were met with hate messages from both girls.
4) My ex's ex-girlfriend in story number 3? Claimed to have depression and an anxiety disorder, and also attempted suicide. One day, my ex puts up pictures on Facebook of the girl with new scars on her arms, and then went mental with people who claimed that it was graphic and shouldn't be on Facebook, telling them that they should care about the girl's feelings. If she's willing to put these pictures on Facebook, she's crying for attention. Personally, I would have said what everyone else was saying, but I've been in a fight with my ex - doesn't end well.