Okay, here's my suggestion. For simplicity's sake, I'm assuming that all "drinks" have roughly the same amount of alcohol - a tankard of ale, a glass of wine, a shot of whiskey.
Each time you take a drink, make an Endurance check. The base DC is 5, plus 1 for every drink consumed previously. Each failed check incurs a -1 penalty to all ability checks, skill checks, and attack rolls (except Endurance checks made to resist the effect of alcohol). When you hit a -5 penalty, you pass out and are asleep.
For each hour that passes, the DC to resist the effects of alcohol drops by 1, and you roll a saving throw. If you make the save, your alcohol penalty is reduced by 1 as well.
Under these rules, an "average person" - no Constitution modifier, no training in Endurance - reaches a 50% chance to pass out around the 10th or 11th drink. (Remember that these are drinks over the course of a single hour.) A character with a +5 Endurance modifier reaches a 50% chance to pass out by the 15th drink, and each +1 thereafter increases your capacity by one drink. Not being a drinker myself, I'm not sure how appropriate these are - I'm estimating based on a Google search on the effects of alcohol - but you can adjust the base DC up or down as seems indicated.
On a slightly different note, I'd be careful about "punishing" your players for having their characters get trashed. Role-playing a night of carousing is a great way to let off steam; no need to regularly interrupt it with attacking monsters. Of course, if they're getting trashed while adventuring, that's another story - but even then, if it's one character who's always slightly drunk, you might consider letting that character be a "drunken master" type who can function at full capacity while tipsy.
