Top Definition
The sudden, often irresistible urge to do something incredibly stupid.
Because third nipples are so weird and unnatural, they cause people who have them to do weird and unnatural things.
A good excuse for doing something weird if you do have a third nipple.
"Jonny, WHY did you stick your foot in that glass jar?"
"Third nipple impulse! I couldn't help it!"
"Why did you walk around with it like that?!"
by Mrs. Horrible November 23, 2008

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