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1.
A blotch of menstrual blood, which has either breached the vaginal wall, or penetrated beyond the tamponial dam. The blotch of menstual blood will then be a permiating stain upon the pantaloons. The jellystain may be odorous, and or damp, be weary of these cautions.
"Woah, you see that jellystain?"
"She walked up and all I smelt was the jellystain!"
"She was dancing all up on me, buttering my thigh with her jellystain!"
"I knew she had lost it all, when the jellystain erupted forth from her pantaloons, oh the stench."
"Im so thirsty man, I'd milk a jellystain."
"She was so nasty, her downstairs was littered with peanut butter and jellystain."
by Nicholas.Ridiculous March 10, 2010
 
2.
The more intense version of the sun patch. When the ass recieves a blow so hard that it becomes bruised for several weeks. The purple color gives it the name "Jelly Stain".

Usually seen among s&m and bondage lovers.
"That Jelly Stain looks like Rosie O'Donnell's fat ass, man."

Chris: "Dude, did you know that Rosie O'Donnell is notorious for her sun patches and jelly stains?"
Kevin: "Yeah, on the news yesterday it said she gave Ellen DeGeneres a fat ass jelly stain on the set of THE VIEW."
by FunestoCartel September 15, 2006