1 definition by NecroManzie
When someone is sexually intimate, or develops an incestuous relationship, with his or her own twin.
1. "The McPoyles from 'It's Always Sunny in Philadelphia' are definitely guilty of twincest."
2. Person A: "Dude, did you see those two guys going at it? They looked exactly alike!"
Person B: "Yeah, man, didn't you know? They're in a twincestuous relationship."
2. Person A: "Dude, did you see those two guys going at it? They looked exactly alike!"
Person B: "Yeah, man, didn't you know? They're in a twincestuous relationship."
by NecroManzie September 27, 2009