On the whole, supervillains aren't exactly a friendly lot, either because they're evil and thus hate everyone ever, or because whatever drove them to villainy also taught them that making pals is a bad idea.
But any practical bad guy is also aware of the benefits of forming allies, and thus supervillain groups aren't as rare as you'd initially anticipate. In fact, even the worst of the worst have done a smattering of tactical team-ups, creating some delightfully deadly combinations - and some really, really unexpected character combinations, because it seems that almost every supervillain has worked together at some point or another.
Although they're often teams that are just as likely to beat each other up as their supposed enemies, many teams of villains have gained some serious infamy - especially those that have existed for long enough to really feel like part of the universe, instead of a convenient way to have two scary dudes somehow work together.
While these villainous teams rarely win, they always leave a trail of blood and destruction five miles long behind them, which is a victory of sorts.