Someone that is negative, doesnt look at the bright side of things and complains
Candace: I hate everything about everything, i dont want to go tonight
Adam: You never want to go anywhere and you always complain, you are such a negative nelly.
The thing idiots say when they mean to call someone a negative nancy.
Cait-"You're such a negative nelly" Everyone Else-"Cait you moron, it's negative nancy"