Riding while drunk, if not totally impossible, is, at the very least, difficult and really inconvenient, and possibly very dangerous. The only upside, really, is that if you ride drunk, you might kill yourself, but probably not anyone else. Driving a car drunk is another matter.

That said, I admit I often frequent pubs by bike, mostly because, being car-free, there's no other way; it's also more fun that way. The trick is to stop before you're too impaired to ride effectively. For me, that's two beers, maybe three if I eat a lot at the same time.

A previous poster mentioned that riding sobers you up. I beg to differ. I don't allow this to happen to myself any more, but when I was younger, I noticed that when I drank a bit too much, but was not yet legally drunk, and got on the bike and hammered away, by the time I got home I was hammered, too. I think this happens because when you exert yourself you metabolize more alcohol more quickly, and it literally goes to your head.