Declaring yourself the winner in the middle of a petty, nonsensical argument by stating, "I win". By doing this, you are officially the winner of the argument in question. This rule is named after Christopher Columbus, who declared that he discovered a country he did not in fact discover, but still receives the credit for doing so.
Cole: What are you talking about? Just because I'm black doesn't mean I love fried chicken!
Stephen: Yes it does. I win.
Cole: What?! You can't do that!
Stephen: Yes I can. Columbus rule. Suck it.