Something that does NOT come out with just shampoo. Very sticky, irritating, but not flammable
Hey harry, this protein stain tastes nothing like caviar!!!
by Zack Morris February 23, 2005
Spermatozoa that has dried on a fabric or carpet or anything else.
"Damn when my wife sees all the protein stains on our new bed she'll know I've been fuckin' around'
by WILFONG June 11, 2003