The little pieces of crap you discover between your butt cheeks when you go to have a shower or bath.
"Damn, grumblebunnies again! I thought I wiped myself good!" , "Um, no thanks, there are grumblebunnies present!", "Shut up, or I'll smack the grumblebunnies out of yo' nasty mouth!", "Grumblebunnies, ewww!""
A term used when fustrated at a situation or person.
(You are at work and you are already in a bad mood when your boss hands you more work to be done ASAP)