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1.
A motorcycle helmet. Specifically the kind that just covers the top of your head. They are mostly sported by riders on top of a American brand motorcycle, chiefly, Harley Davidson.
Hey Pete, good thing you were wearing your brain pan when that car slammed you. Your face is a mess but at least you can think straight!
by WindowLicker9000 April 11, 2010
 
2.
The part of the skull that encloses the brain.
Bullet to the brainpan. Squish.
by Skalman January 13, 2010