"Lose" is a verb. You can lose your wallet, lose a game, or (like me) lose your mind. Paul Simon even thought of fifty (well, five, but I guess that didn't make as good a title) ways to lose a lover.
A bet you're unlikely to win is a losing proposition. If you're playing Scrabble and your opponent is winning, that means you're losing. You're not loosing. No matter how lopsided the score, you can take comfort from the fact that you're never, ever loosing a game--unless the board is stuck in a tree branch after a tornado and you're knocking it loose.
It's possible to be a loser, but you're only looser if you just practiced yoga.
"Loose" is sometimes a verb and often an adjective and, increasingly, a pain in the neck to proofreaders, editors, and perfectionists everywhere. Because almost no one uses it correctly anymore.
You have loose change in your pocket. Loose clothes don't fit very tightly. The dog slipped his leash and has gotten loose. If you're loosing chaos on the world, you're wreaking havoc. You're only losing chaos if your girlfriend's name is Chaos and she wants to break up.
Tom Brady might fumble, resulting in a loose ball on the field, and the Patriots might or might not go on to lose the game. But the Patriots will never, ever loose a Superbowl. A player can be a gracious winner or a sore loser. Never a sore looser. Though I suppose it could be argued that a battered, injured quarterback who lets go of the ball after being hit by a 400-pound linebacker is a kind of "sore looser."
A zookeeper can lose a Siberian tiger. (The tiger might die, or zookeeper might forget which cage he put the tiger in.) Or a tiger might get loose (i.e. escape), as happened at the San Diego zoo in December 2007. A zookeeper can even loose (i.e. set free) a tiger by opening the cage door, but, well, that wouldn't be a good idea.