The Truth About Beer Goggles
There is quite a bit of evidence that alcohol consumption lowers our standards for physical attractiveness. There is pretty much a consensus that alcohol does this but there is debate as to how. One theory is that we don't really see other people as more attractive post-drink but, instead, the part of brain that makes good decisions is basically shut down by alcohol. This makes us less inhibited and, therefore, more likely to go after a less desirable potential partner.