Found it in the newspaper. Means: puke, vomit, throw up, upchuck, barf, spew, blow chunks, ralph, hurl, lose your lunch, be sick etc etc etc.
I'm always afraid my gf Holly's gonna protein spill when she blows me 'cause her gag reflexes are so fucking bad.
Any bodily fluid that reqires clean up such as vomit, urine, blood, feces. This term is used most often in theme parks.
Nicole: "Hey Thomas, we've got another protein spill in the third car!"
Patty: "God, if I have to clean up another pound of upchucked popcorn I'm gonna quit!"