I want to go with Walt JR due to how pointless he is but I'm going with Frank Burns from MASH. The reason why is because of how poorly he was handled and his charter being just shit. For being poorly handled unlike every main character in the show he never had an episode that's dedicated to him and unlike every character in the shoe we know little about is backstory. He's a main character who might as well be a said character due to the way he was handled.

For the his character being shit he has very little character development to him. Unlike Radar who comes into the show being childlike and leaves grownup Frank had very little change about him. He started off as a dick and he ended up still being a dick but he became worse. He basically is the same character he started out as to his last episode. The other thing that is shit about him is how unrealistic he seems. At first he was military which is believable but latter on he became such an asshole that someone like him can't possibly exist. Instead of starting off hard and getting alone with the others latter on like Winchester he still remained an asshole. When you're forced to be in a war and the only family you have is the people around you I hardly doubt you're going to be a dick to everyone that long. You're going to need friends in order to get by without committing suicide. Besides Margret that's something he hasn't done which is something I can't find believable. 

Peggy Hill

To me Hank and his Family are the worst characters in the show. Luanne is annoying who can be painful to watch at times, Peggy is the same way, Booby tries too hard to be funny which got old fast and Hank is just too uptight.