The Slut: Metroid
Maybe it stems from mommy-issues, but something about the combination of alcohol and dark lighting makes your friend turn into a parasitic monster with a deadly desire to suck face. Metroids will show up at the bar wearing their sexiest outfit, ready to latch onto pretty much anything that moves. And once they're done draining the life out of one victim, they just float to the next, with no shred of decency or self-restraint. They're somehow able to identify and attack the weakest-willed, so make sure you have your defenses up. Unless, of course, you want the Metroid to have their way with you. Just make sure you have a recovery plan ready, because the next morning may not be so pretty.
The Alcoholic: Pac-Man
Pac-Man has been drinking for what seems like forever (read: the eighties). He's got one goal and one goal only: get messed up. Just point him in the direction of a beverage and he'll drink it. Beer, wine, cherry-flavored vodka, whatever. If it's alcoholic and it's within chomping distance, he'll put it in his mouth. Pac-Man's so dead-set on getting obliterated that the only way to have a conversation with him is to chase him into a corner and force him to talk to you.
Another downside? He won't stop until he passes out or dies, so he'll drink you under the table until there's gross strawberry-banana vomit on the floor. Pac-Man might have been fun back in the day, but piece of advice? Only go out with him if you're really, really bored.