My eldest tried that on me, “everyone hates me” at first I tried to talk her out of it IE giving her compliments and telling her how wonderful she is but the problem just got worse then one day I had it and when she came off with the everyone hates me stuff I just told her "ok , everyone hates you this is why you have cloths on your back, food on your plate, a roof over your head and proper medical care is because you are hated soooo much. I left it there, she just sat back with a stunned look on her face and finnaly said “wellllll mom I didn’t mean you!” I popped back at her “well I guess not everyone hates you then, huh?” That is when we got down to the real problem she was having.
I loved the “its not fair!” stuff too. I would just pop back with " you did this and this soooo you want me to give you whats fair?" funny I never did have any takers for that. The trick is to make them realize the part of the cup that is half full. I found that the best thing is not to play into self pity or self anger but to call them out on it.