We know squirrels hibernate, and they dig in the dirt to hide their nuts... So... The Hibernating Squirrel is when you are doing a chick doggy style in the ass(Digging in the Dirt) and you tuck your balls inside her vagina (Hide your nuts)
The act of taking a crap in the cistern of the toilet. The turd then hibernates for a couple of months before being broken down enough to emerge during flushing.
Person 1: OMG i just flushed the toilet and shit came out instead of water
Person 2: Dude you awoke my bear, it's been hibernating for the last 4 weeks
Person 1: You did a hibernating bear in my toilet...you're seriously fucked, we are not firends anymore