Sure, we come in peace and all that. But sometimes, when we encounter alien life forms, the only way we can communicate is by using our built-in universal translators: the ones with five knuckles and a thumb. Here's our compilation of the greatest scenes from movies and TV where a human socks an alien. (To the tune of "Mama Said Knock You Out" by LL Cool J.)
Thanks to Lauren Davis for all the research help.