Top definition
A condition found in animals from the planet earth(primarily humans)in which the animal loses the ability to NOT speak every single word they are thinking. The verbal words are spoken about 1/trillionth of a second (actually faster than the speed of light) after the thought of the words in the brain itself.
Dad walking down street with 3 year old daughter bump into an extremely overweight acquaintance of dad's.

Dad:"Hi Lyndon."
Lyndon: "Hi Chuck."
Gracie(3-year-old daughter poking finger into Lyndon's large soft belly):"Mr. YOU have a FAT tummy!"

Gracie would at least momentarily be experiencing "Brainmouth".

by Squarezup September 20, 2008
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