I know it's looking ahead a bit, but......
I reckon a Jamacian will win the 100m (either Asafa Powell or Usain Bolt). I'll happily take an avatar bet with anyone who thinks an American will win it (most Americans will probably say Tyson Gay which is fair enough).
If any Jamaican wins; I win
If any American wins; You win
If someone else wins; Neither of us win
I'm taking Asafa, so I can't take this bet.