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1.
The best sentence or sentence-filler ever.
"What have you been doing?" "Mumble mumble."

Welcome to asperger king, where your extremely specific fast-food order is our mumble mumble.
by white brown! May 04, 2010
 
2.
Radio edit substitution for "motherfucker"
Do the ladies run this mumble-mumble?
by Ross Hogg September 24, 2002