rusty underwear

Underwear that has been worn and when taken off has a brownish shit stain on it.

i dont let my mother wash my underwear because i always have rusty underwear

by Miguel Gonzalez March 29, 2008

rusty undercarriage

Someone who doesn't like to wipe after a fat shit.

"I heard he has a rusty undercarriage."

by Onethatpeoplehaventusedyet August 3, 2014

active undercarriage rust protection

Marketing-speak for a chronic oil leak on your automobile - generally one that takes more effort to fix than the car is worth. Comes standard on most General Motors products since the early 60s, as well as Saab 900 series.

Click: Dude have you seen that grease spot on your inner fender?
Clack: Oh don't worry about it, that's just active undercarriage rust protection. Paid extra for it. I think.

by Buick Roadmaster June 5, 2011