“Dude A totally looks like Dude B” threads have probably been done before, but I just had to point this one out. Every time I see No Ordinary Family I get totally creeped out by this guy who plays a bad guy or something on the show. His hair is darker on the show and so he bears and uncanny resemblance to Glenn Quinn who played Doyle on Angel and Mark on Roseanne.
Glenn Quinn died a bunch of years ago, so this other guy, Josh Stewart, gives me the heebie jeebies.
That reminds, on “Seinfeld” the actress who played Jerry’s nudist girlfriend looked an awful lot like the singer Jewel (albeit without the snagged teeth).
Not quite what the OP was thinking of, but there was a lesbian couple at a party I went to last year, and both of them bore an uncanny resemblance to Michael Cera. Kind of disconcerting.