A tnarg is when you sleep with a member of the opposite sex in its purest form. While non sexual, it may include spooning, snuggling, and cuddling. This typically occurs between friends, people who are very cold, or when a lot of people sleep at the same house and there is no extra room.
There was no extra room on the couch so Cleo and Rebecca got their tnarg on in his bed.
If I didn't know any better, I might say Larry is an avid tnarg enthusiast.