twincest 

incest between twins.
twins who have a sexual relationship

Benji madden + joel madden = yummy twincest

twincest by squee February 19, 2005

twincest 

sexual relations with your twin

lucy and anna were twins but they regularly ate eachother out. this is called twincest

twincest by anonimus 1/\ December 1, 2007

twincest 

Incest between twins. In the world of fanfiction, this is both a frequent and yummy occurance that we, as human beings, should be eternally grateful for. <3

Hizashi/Hiashi is mad twincest. <3

twincest by Louey March 28, 2007

Twincest 

The act of Incest between twins.

"I can't believe those twins are snogging! That is blatant twincest"

Twincest by Joey Masters January 2, 2008

Twincest 

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!"

Twincest by epsilina August 4, 2007

Twincest 

Stuff you say "woah, that's sexy" to.

Woah, that twincest is sexy.

Twincest by Kat-chan February 1, 2008

twincest 

Twins having sexual relations. Capeesh?

Tom and Bill Kaulitz (Tokio Hotel) have twincest time on the tour bus every night.

twincest by anonymous twc fan February 28, 2009