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1.
noun.

A penis whose primary characteristics are defined by it's inability to reflect any perceptible amounts of light towards a human eye due to its extremely diminished stature. Thus being only perceptible by mechanically or computer aided viewing devices such as a microscope.
Micropeens are so small they make me laugh.

I can't see your micropeen.

Apparently a micropeen was on my leg, but I could not feel it.
by G-Noles March 10, 2010
 
2.
Short for micro penis, but is used to describe someone or something that is lame, goofy, or just a straight up douche bag.
That person who just drove by me in that Honda civic with the overly loud exhaust system is a total micro peen!
by Earl Clemintine June 12, 2013
 
3.
Adjective for a very small penis.
You have a micropeen.
by jenk February 23, 2005