A really torn-up asshole. A combination of the words "wreck" and "rectum."
"She liked it so much that I decided to give her a wrecktum."
Wrecktum = wreck + rectum. Usually a reference to anal sex.
My son, Will, used to be a heterosexual. Butt, when he was in prison, they wrecktum. I should have gave him some Soap-On-A-Rope.