As far as ugliest rock star goes ... that's kind of an oxymoron, 'cause most guys (especially guitarist) become rock stars because the ARE so ugly. But, for the sake of argument - there is no argument.
Hands down, ugliest guy is Shane MacGowan, singer/guitarist from the Irish punk(ish) band The Pogues. (And please keep in mind - this is a glamour shot!)
Second place goes to Angus Young. Dear God, the man's named after a cow (or the cow's named after him ... either way it's bad.
Then there's Lemmy of Motorhead. But he's ugly/cool, plus the greatest mole in rock