When a girl wipes back to front and pieces of poo get stuck in her pubes.
I was about to go down on this girl but I realized she had mad mud crotch, so I said, "hell nah, put your pants back on and get the hell out, bitch... unforgivable!".
when someone hasn't showered for a couple days, has done some serious sweating, basically been able to wash their crotch for an extended period of time
"Man, Jill was all about messing around last night but I had just got bad from the gym and had nasty mudcrotch"-Chris
"How was the camping trip?"-Chris "Meh fine but after not showering for three days Stacy had some mad mudcrotch, and she kept wanting me to go down on her"-Rory
Boys who enjoy yaoi (a genre in Japan that contains sexual and/or romantic relations between two men); literally translates to "rotten boy"; corresponding female : fujoshi