3. Sheldon Cooper
Sheldon Cooper has the "honor" of being one of the few characters who single handedly managed to destroy an entire series. At the beginning of the series he was a weird and smart character who somehow managed to be charming and likeable at the same time. It was no surprise that the writers would try to take advantage of the character at any cost. Even if that cost was the destruction of the entire show. They decided it would be smart to take those things that made the character funny and give them steroids. Exaggerating a character's traits and attitude won't make it funnier, in fact it will kill what used to be funny and replace it with an annoying piece of crap. Things got worse when they felt it was necessary to add a female counterpart to him, which its as funny and as enjoyable to watch as a documentary about the war crimes in recent years.