Hygienically challenged, usually overweight, people can develop a residue of body secretions on their person, typically in compressed areas of the body described as "folds". It can also accumulate in the groin. This filmy substance has a distinct and unpleasant odor. Like crap.
I would go on a date with Tina, but damn she smells like flap crap. I don't want to get that stuff on my hands.
I gave Cortney a lift home, now my whole car smells like flap crap.
One who masterbates in his/her own fecal excretions; usually someone with mental retardations or an individual who has problems with standard/orthodox masterbation.
"Hey brah, you need to wash your sheets; were you eating sundaes in bed and watching television?"
"No, I was actually masterbating in my own butt squirts."
"Oh okay, that is gross, your a crap flapper you are."