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1.
A girl that is a slut and more than likely has some sort of STD. Usually this word goes hand in hand with mud shark, because most filthy whores like black cock.

"Oh my god dude, I hope you had a rubber on for that dirty butt."
by Gary from 405 November 30, 2007
 
2.
Someone sporting a Venereal Disease. These are the ones that can often be found attempting to spread said Venereal Disease via the act sex while not informing potential sexual partners of their dickrot, or vagrot.
"Ol' dirtybutt scored him another one last night!"

"Another girl?"

"No, genital warts."
by Brian Saunders October 19, 2008
 
3.
Any female who sleeps around. It is a widely known epidemic. Girls who are classified as Dirtybutts are also known to carry one or (usually) more STD's. They are known to fuck multiple guys in one night, and countless throughout the week. They will drive any distance at any time to get their fix.

Also known as "DB" for short.
That bitch is a dirtybutt forsure. She fucked both of my roommates and then tried to come onto me.

That bitch needs some TP for her DP... Actually, she needs straight diaper wipes.
by YOLOMUTHAFUCKA September 19, 2012
 
4.
A person that wears the same thing more than once a week. Or wears dirty clothes and busted shoes...a person that is very much capable of getting new shoes and clothes and taking showers but insits on looking like a homeless person...
Man, didn't Brandon wear that outfit yesterday?
Yea...look @ tha grass stains on his shirt!!!
Man dat nigga is a dirty butt!
by Ne-Ne October 02, 2005