Sacrificing a creature I control that my opponent owns
Because Magic has physical cards worth money, they go to some lengths to ensure your cards don't accidentally end up with another player. So there is NO way one of your cards ends up in another player's deck, hand or graveyard. (The other zones are shared.)


  400.3. If an object would go to any library, graveyard, or hand other than its owner’s, it goes to its owner’s corresponding zone.


That said, things don't get that far in this situation. Sacrificing instructs you to place the card in its owner's graveyard.


  701.16a To sacrifice a permanent, its controller moves it from the battlefield directly to its owner’s graveyard. [...]


There used to be an exception when playing for ante, but that doesn't exist anymore.