While I'm not a big fan of the way Tim fights since he's become champ, and don't think you can say he doesn't deserve the title. Is he champion in a weak division? Sure. Has he bored the hell out of everyone since beating Andrei last time? Sure. But he's champion because he won the title, and you can't take that away from him.
To say Sherk doesn't deserve the title is just silly. The lightweight division was just starting again and Florian were good choices to fight for the belt. Jens had just been knocked out by a newbie, and B.J. was still a weltereight.
This is going back a long way, but I think the single most undeserving champ in UFC history has to be UFC 3 champion Steve Jennum, the "ninjitsu" guy who won the tournament with one fight against a gassed Harold Howard, after Shamrock, Gracie and Hackney all withdrew.
That was F'n ridiculous. But it was fun to watch Tank nearly pop his head off at UU 95.