It's when your roommate is taking a shit but you also have to shit you shove them off the toilet and you both hover over it, evacuating your bowels simultaneously.
"So how was the dinner party last week, Ted?"
"Oh it went fine, until Bridges brought out the pâté. Heard there was a shoverhover going on in the upstairs bathroom. It got...everywhere"
The couch was littered with Frito detritus, a laptop opened to the Wiki for Game of Thrones, and a set of fuzzy socks, while a Roku screensaver bounced on the TV: it's clearly shoverdose.