Mumbly Grumbly 

Term used to describe someone who complains, bitches and moans all the time but does it in a low 'mumbled' voice, and in low, run-on sentences so you can't understand what they are saying.
Usually, but not always, limited to grumpy old men.

That old dude looks mad, and keeps mumbling something, but I can't understand him.
Yeah that's old man Withers...he's always all Mumbly Grumbly.

Mumbly Grumbly by phoenixxx70 May 14, 2010

mumble-grumble

the need to take a massive intense shit

ive been holding this mumble-grumble all day.

mumble-grumble by theinventorofthemumble-grumble September 20, 2012

Grumble Mumble 

verb - it is when a person shakes his/her head looking downward with a melancholy look on his/her face while making a soft grunting sigh

John: Why are you so lame?
Sunny: *grumble mumbles*

Grumble Mumble by bapsiboy February 19, 2015