Top Definition
An imaginary (yet vital) loose part hanging from underneath an unsuspecting motorist's car. Alerting unsuspecting motorists about said item is of supreme importance. Mission accomplished when unsuspecting motorist pulls over and gets out to see whats wrong with his car.
Driver 1: (while pointing at undercarriage) "Hey Sir, your Fister saster caster unit is out"
Driver 2: "What"?
Driver 1: "Your fister saster, the caster unit, it's out" (still pointing)
Driver 2: "oh really?!? oh, um ok" (pulls into rite-aid parking lot)
Driver 1 then laughs laughs laughs all the way to work.
by Mergeman August 05, 2008
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