hallcest 

Having intimate relations with a person residing in the same hall of your dorm/apt/etc.

Person1: "Hey, Molly is really hot."
Person2: "No way man, she's only three doors down. That's like hallcest."

hallcest by Anonymous March 27, 2003

Halfcest 

Halfcest is like incest, but between siblings who only share one parent.

guy 1: Hey so did you fuck your sister last night?
guy 2: She’s my half sister, and NO! That would be halfcest

Halfcest by Freezergoat July 2, 2018

hall-cest 

going out with people from one's own living group

hallcest often results in bitter exes living next-door to each other, dating each other's exes, in a vicious cycle.

hall-cest by pysanka June 10, 2005