Rigby is the epitome of grumpy and out of luck.
Everything he does seems to backfire on him.
And what's worse is he's hopelessly in love... with a girl that has no interest in him whatsoever.
Quite literally. She's a lesbian.

So... yeah. Poor guy. Can't blame him for hating the world.
Or Trixie. Since she's the one that's with Cuckoo. The one he loves.

Mmm love triangles but not really.