Man Eating Flesh Disease. STD. This is usually passed from somone who cannot count their number of sexual partners on their fingers and toes. It kills the tip of the penis and works its way to the butthole.
"Wow.. did you hear what happened to Sam, Brandon, Zag and Tyler?"..."Yeah I heard they had sex with this one girl and contracted the MEFD"
Or it may be used in the form of an adjective, "Yeah Mel totally MEFD those guys..."