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A short form of Assassin's Creed: Brotherhood, a historical fantasy third person action-adventure video game developed by Ubisoft Montreal. Also sounds like a crude sexual reference for the uninformed.
Played some solo ASSBRO last night. Ya know, to practice.
by NotScottKurtz November 23, 2010
Gay guy 1: So Brad and I are screwing every night now.
Gay guy 2: Are you guys dating?
Gay guy 1: No, he's afraid of commitment. We're just assbros.
by Canopenerdude December 01, 2013