8. Charlie Sheen
Charlie Sheen is the former star of one of Chuck Lorre's other works, Two and a Half Men, so it's only natural he might've made an appearance pre-breakdown. However, it's by far the shortest cameo on the list, and if you blinked you would have missed Sheen's seven words in season two's 'The Griffin Equivalency.' With Raj nominated for People Magazine '30 to watch under 30', the world of executive dinning rooms and lackeys goes right to his head and causes him to alienate his friends. After the gang leave Raj alone in The Cheesecake Factory, he needs someone else to show off to. Unfortunately, his choice happens to be Charlie Sheen, who simply replies with 'call me when your on the cover.' The fact that there was no hint at the cameo just makes it so good it literally comes out of nowhere.