What is the difference between being dour, being sulky, and being a complainer.?

Dour is a personality trait. Sulky is an attitude and complainers are a pain in the azz. To be all three is a good way to get yourself tossed. Whenever you think dour also think sour and you have the expression that a dour person wears. Sulky is a "woe is me' type of thing.