Complaineer

A complaint engineer. Someone who will ALWAYS find things to complain about.

No matter how good or bad things are, they will always complain about something and feel like the world needs to know. Will get irritating to listen to very quickly.

"He literally just won $10.000 at the casino, and still think the world owes him everything, complaining about any and everything. He will literally never stop complaining, even when things are not that bad. He is a complaineer."