The dry rusty colored shit around your asshole when you dont wipe well enough...it really burns and its hurts making it hard to move...it also hurts extremely bad when you take a dump if you already have it...the best way to get rid of it is with some wet TP or paper towels
Dude...i can't move...my butt rust hurts...ahhh it burns
by butt sex April 15, 2007
The off-brown discoloration inside the undershorts. Butt rust, also known as "skid mark" is usually the result of high pressure farting and / or lack of sufficient wiping of the anus.
"Damn, Frank sure has butt rust on his undies here."
by Frank Klaune March 05, 2004
It's when you don't wipe your bum good enough after taking a poop. Your bum can get poo crusties and make your asshole itch.
I've got a bad case of butt rust this morning after all that drinking and pooping I did last night. Poop.
by MrRoche May 18, 2005
is when one neglects to clean or wipe properly betwixt their glute cheeks and a flaky orange/brown build up of poop deposit happens. Butt rust has been known to emit a foul odor of human fecal matter and cause extreme and even painful discomfort when walking, running and especially biking. Butt rust is not only a human malady but is most common in and among other bipedal or quadrupedal mammals whose legs come together near the exterior of the anus to form a crevice or fissure of the body perfect for the formation of said ailment. Butt dust can often be embarrassing as it can appear in your undergarments as skid marks, it can leave behind butt dust (see butt dust definition), or it can cause grief and later chafing when one is expecting to expect butt sex. The only sure fire ways to rid oneself of butt rust is to clean between the buttocks thoroughly and regularly and to perform extra in depth wipes after leaving a deposit in the porcelain pot.
"After not bathing for a few days I was washing my tush in the shower when I noticed the water turned an orange/brown color which must have been from my butt rust."

"I was going down on Tammy the other day when I accidentally licked her anus and she had butt rust there!!"

"I didn't know what to expect when having butt sex but I knew I needed to take care of my butt rust before the main event."
by butt_bot September 12, 2011

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