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1.
A sexual text message sent/received by a relative, in hopes of invoking sexual relations. (A sext to/from a family member.)
"Eww, I read all the texts sent from Anna's brother to her, they were all insexts!"
by Shandi1337 May 10, 2010
 
2.
The act of sexting a close relative. Derived from the word "incest"
X: (Sends sext) Who's your daddy, baby?
Y: Dad, I told you to quit it with the insext. It's kinda gross.

X: I heard that Joe got arrested for insext with his 17-year-old niece.
Y: What a mess.
Z: That's what BP said!
by Hamfry May 23, 2011