I'm going to go with Luke: Didn't he say he was a demigod?
While fighting Alucard.
If he was fighting someone on a comparable level to himself, whom he actually had a chance of beating, I'd pick someone else. But since he was fighting Alucard, and knew full well his reputation, yet STILL talked himself up, I'd say that's more ego maniacal than anyone else on this list.
Everyone else actually had a chance, or even an advantage, that would offer some justification for their ego. Vegeta was constantly training, Kira actually WAS smart enough to get away with it, Yami really WAS that good, Ben's got an infinite number of superpowers at his disposal, Aizen came REALLY close to pulling off his plan, etc.
While I'm not familiar with Hagire, I'm pretty sure Luke's the only one who not only had no chance of beating his opponent, but knew his opponent's reputation extensively PRIOR to challenging him.