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1.
When someone is afraid to say what they want, so they mumble it. The person nearest to them then shouts "Mumberlaaa" in their face.

Or when someone is saying something you don't agree with but you have no real argument and resort to shouting it in their face, claiming you cant hear what there saying.
Teacher: WHAT DO YOU THINK YOUR DOING!!
Guy: Errrm, I was just, errm nothing its, I was..
Guy sat next to him: MUMBERLAAA!!
by GyratingJack August 28, 2010