1. To aggressively perform anal sex, as if one owned, or pwnd, the butt involved.
2. To express domination in a non-sexual field in this manner, whether or not actual penetration occurs; an augmented form of pwn. To pwn completely or utterly.
Pronounced 'buttpown'. Also, "asspwn" or "pwn butt".
1. I'd totally buttpwn someone if they brought me a pizza right about now.
2. With a sniper rifle and a thermal scope I can buttpwn the whole other team.