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The leader of a pack of bros; inspires the worship of subordinate bros through being slightly more articulate and much more aggressive, and having both a higher alcohol tolerance and better luck with the bro hoes.
At a frat party:

Rachel: What's the matter with all the bros tonight? They seem subdued.

Sarah: Yeah, Vinny's not here. They're totally lost without their alpha bro.
by ameech November 05, 2009
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