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)
In addition to being a situation in which two people date so exclusively that you rarely see them, the hiberdating couple will make occasional public appearances. During these appearances, the two will never acknowledge anyone but each other, never stop touching/caressing each other, and will annoy the living piss out of anyone and everyone in their vicinity, especially used-to-be friends of the hiberdaters.
Wanna go hang out with Kenny and Marissa?" "Sure, if you want to puke your guts out listening to them talk goo-goo to each other... they've reached hiberdating status ever since Kenny refused to take his hand off Marissa's knee during Science class