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 28, 2009

by Rhiannon December 08, 2003

Incest between any set of multiple birth siblings. Twincest can occur between twins, triplets, octuplets, etc. Twincest may also occur across gender lines (sisters, brothers, or both). Twincest can be any level of sexual intimacy.
by T-Winner July 10, 2009

In The anime/manga series Ouran High School Host Club the Hitachiin twins(Kaoru and Hikaru) were called out on there twincest by Kirimi Nekozawa.
by sourxneonxgummixworms June 14, 2009

by Joey Masters January 02, 2008

There is often fanfic involving twins such as Fred and George Weasley having sex.
"I just read this really odd fanfiction that involved a lot of twincest!"
"I just read this really odd fanfiction that involved a lot of twincest!"
by epsilina August 04, 2007

by Kat-chan February 01, 2008
