Seven Guest Stars Who Blew Our Minds on The Big Bang Theory

Charlie Sheen! Stan Lee! Bill Nye! Watch our favorite surprise celeb moments from the series

CHARLIE SHEEN

In happier times, then Two and a Half Men star Sheen agreed to make a cameo in creator Chuck Lorre's other hit show on episode 4 of season 2 (prior to their very public falling out). In the episode, Raj (Kunal Nayyar) finds out he's been named one of PEOPLE magazine's '30 Visionaries Under 30 Years to Watch,' gets a little too cocky and brags to a stranger who – surprise – ends up being Sheen. "Call me when you're on the cover," the unimpressed actor deadpans. Ouch!