A good way to gauge whether or not a fighter to deserves to make this thread is if he's "embarrassed you" in front of a layman fan.
If your casual fan friend is seeing ______________ for the first time after you'd hyped the fighter up saying "Oh man! Wait until you see ____________! He's so badass!" but the fighter comes out flat or tentative as can be and makes you look like you don't know what you're talking about, with your friend saying "I dunno, man, wasn't that impressed," then he fits this list!
My biggies are Cro Cop and Wandy but another guy who's made me look silly of late is Rich Franklin.