To completely foul up a project by making the most boneheaded mistakeone can make.
Dude1: Holy shit my computer won't boot up WTF is wrong with it?!
Dude2: You idiot you bolted the motherboard directly to the case!
Dude1: Huh?
Dude2: MOUSEY'D
Dude1: *dies*
Someone who is a technical specialist. A mousey would seep into small areas in a computer and fix the problem.
A mousey has also been known as an urban myth to summon bears at a certain age.