Drinking heavily, when one has an angelic alcohol tolerance, is easier said than done. So far his drink is having about as much effect as half a pint of beer, so it's not that irresponsible. What would be irresponsible would be offering it to people on whom it might have more of an effect. Castiel's alcohol tolerance probably isn't a great deal less than Gabriel's, but he offers it anyway.

"Yep. Nothing like a party to make the season tolerable. Although I'm beginning to suspect she completely forgot the strippers, which is a shame."