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When someone who know starts acting like a complete jackass, when normally they're not.
Person 1: "Did you see that chick last night?"
Person 2: "Yeah, wasn't she hot, too bad she's Rachel's cousin..."
Person 1: "Rachel's my girlfriend! What's wrong with Rachel?"
Person 2: ".... Nothing.."
Person 1: "Why you being so Jackassish?"
by StarDust July 23, 2013
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