Slang for having sex.
Origin: Unicorns of myth reputably could only be tamed by virgins. So, were a man or woman to kill the unicorn they would be slaying the metaphorical virginity. Used in everyday situations it is simplified to having sex.
Guy 1: Dude? What are you doing tonight?
Guy 2: Oh, you know, going to my girlfriend's house. We're killing the unicorn.
by elemenopee March 13, 2009
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