There are certain multi-player video games that I connect to specific times in my life at which those games were the most fun. Trying to pinpoint the best of all of them would be maybe impossible, and I might be cheating in choosing two, but these are tops for parties.
In college it was Mario Tennis (on GameCube). It was probably the competitive group of 15 or so regular players and the fact that I wasn’t horrible that made it so awesome. More recently, I really enjoy Castle Crashers, which is more button mashing and casual as well as fitting for a group that enjoys their alcohol.