1. A pirate whose preferred method of pillaging is though the backdoor.
2. Someone who engages in the giving of anal sex.
3. A common name for a hypothetical homosexual piece of pornography. However there is no evidence to suggest that there is either a movie or a magazine which has the words "Backdoor Pirate" anywhere in it.
Rodion: "I am a backdoor pirate."
Joey: "HAahah I bet your dad stars in Backdoor Pirates 7!"
Rodion: "You fucktard...there's no such thing!"