People on ImgFlip can be mean for multiple reasons. Some may be going through tough times and want to brush it off on others to make their own pain go away instead of just talking. Others just want to be mean, as you don't know who they are and that then just makes it easier for them to bully their victim. They may not agree with a meme if it an opinion or anything that someone may not agree with, which is quite annoying because everyone has opinions. Some do it simply for fun which is just wrong, with no reason behind it. Everyone has their different reasons for being mean, which can be from them having their own problems to them just being someone who is a narcissist, only thinking for themselves.