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."
by NecroManzie September 27, 2009
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When Twins are in love with one another and/ or like to perform sexuall activities together.
Benji and Joel are in alot of Twincest fics.
by Rhiannon December 8, 2003
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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.
The Visconti triplets practice twincest in homosexual pornography.
by T-Winner July 10, 2009
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the hottest damn thing ever!
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
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The act of Incest between twins.
"I can't believe those twins are snogging! That is blatant twincest"
by Joey Masters December 7, 2007
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A form of incest between twins. Twins having sexual relations.
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!"
by epsilina August 2, 2007
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Stuff you say "woah, that's sexy" to.
Woah, that twincest is sexy.
by Kat-chan February 1, 2008
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