Frat Boy Fail Share definition Flag When a Frat Boy screws up, so much so, that his brothers wouldn't want to claim him. Girl 1: "Did you see Johnny totally frat boy fail last night?"Girl 2: "Yeah, he puked in the bar. What a light weight!" Frat Boy Fail by UNIMAGINABLE21 December 17, 2009 Get the Frat Boy Fail mug.