Sofa Butt

The pain you get in your ass from sitting on it all day. Discomfort can also be in the lower back.

This was referenced in S06 E21 of the popular TV Show "New Girl" (2011-2018) when Jessica Day, suffering from heartbreak, refused to leave the house.

"Let's just get you out of this house"
"Yeah, right"
"Well what are you going to do? You're gonna sit on this couch all day long? You'll get sofa butt. C'mon, let's go get some ice cream."