If you don't mind ruining friendships, Mario Party is - as the name subtly implies - a party game. Granted, you win by being the supreme asshole on the playing board, but if you and your friends are drinking, it's just drunken fun :)
(this from somebody who does not, has not, and has no intention to, consume alcohol)

Barring the above and the aforementioned Just Dance and Rock Band, there are actually quite a few games on Nintendo consoles that go well with parties. Mario Kart would be fun to watch drunk people play, but only if they're not the kind of people who will play a game while drunk then go "I'm gonna go do that for real now!" That's how drunk drivers die, so please prevent that to the best of your abilities. Another good one is Super Smash Bros. Brawl, and later in the year, Super Smash Bros. for Wii U may also be good for parties. I know the former has a rotation mode specifically meant for when you've got a lot of people playing, but am unsure if SSB4 will have this feature on Wii U.

Sadly, I don't go to parties, so the best I can do is offer up some games that would be good for them.