1) v. To seat pirate is to take someone's, usually better, seat when they get up to go to the washroom, get a drink, et cetera.
2) n. One who pirates another person's seat.
3) n. One who prefers anal sex, specially if they pursue it agressively.
1) When Dan got up to get the phone, Robbie seat pirated him.
2) Hold my spot on the couch, Robbie's a total seat pirate.
3) Gary may look like a bottom, but he's really a total seat pirate.