It seems that single people hate couples and couples hate single people. Why? Well, it may not be why you think. 

It's actually because of consistency. So, those that are single probably have been that way for long enough for it to feel like normal life to them Those that are coupled up also probably have been for a while and feel the consistency in that.
So, even if you're in a crappy relationship or you are single and really want to get together with someone your brain is making you feel differently.
There's such a difference in each lifestyle that depending on which side you're on that you're not going to be cool with the other lifestyle.