Fighting Fedor moust have been scary. The aura that came with him, considering how unassuming he looks is just unbelievable.

Hendo for his punch. One look at his right hand would make me crap my pants.

Always thought Rampage looked a scary dude.

Also, Kimbo Slice looks scary because he looks like a homeless bum, and you could never be sure what kind of weapons he'd fashioned while living on the street.