I suppose it doesn't help that his guardian angels of drinking (for lack of a better term) are extreme attitudes about alcohol: D.A.R.E. and Peter Griffin. The former-even years after middle school-still haunts Chris, and he'll be quick to tell you that excessive drinking is a bad, bad, bad thing. But at the same time, the latter has shown Chris that excessive drinking makes you the life of the party, talented, balls-out funny, and with no consequences to face afterward (or at least no consequences that can't be solved with a heartfelt speech accompanied by soft underscoring).
And, like others have said, it also depends on what Chris is drinking to excess; there's a big difference between Bud and, say, Arrogant Bastard. And again, not to mention that he's gotta lotta fat on him to absorb everything.
So when Chris tries to get out of a tight spot with an "I was drunk" excuse, not only does he admit to behaving like a criminal, he sounds like an idiot.