At one point Donald got on my nerves because I couldn't understand what he was saying half the time and he has a crappy personality, but Donald is an unoriginal answer, I gotta think about it more...
Frollo. The guy is such a douchebag and completely unlikeable. A character that I love to hate. Sarousch was a hell of a lot more likeable and was funny too.
If Disney Channel, Disney XD, or Disney Junior characters count, then, I say Pickle and Peanut from the Disney XD show, "Pickle and Peanut" are the most annoying characters Disney has ever created, if Walt Disney was still alive, I think he would be horrified if he saw this show.