Why do people excuse their behavior when drunk?

Once in a while, you can use the excuse that you drank too much if you did something that was out of character for the first time. I think everyone gets that get-out-of-jail-free-card. But if it's a pattern, and it happens enough to brag about it, then that person clearly is to blame for not controlling their drinking. If you know that you tend to get in fights after 12 tequila shots, you should probably stick to 11. It sounds like he's proud of it so don't expect that to change any time soon!