A phenomenon occurring in one's hair in which lettuce is induced by sweat. When one who does not normally have flow suddenly acquires lettuce due to massive amounts of sweat. Often frowned upon by those who actually have flow and dedicate large amounts of time to develop their lettuce, such as lacrosse and hockey players.
For clarification, lettuce refers to the flow at the back of ones head that flows out under a hat or helmet. Flow refers to long, curly or wavey hair that would flow out the back of someone's helmet and curl up around the back of the helmet.
Brad: Bro I sweated so much when I was grinding up on those slam pieces at the club that I developed some dope sweattuce!
Troy: That's so chill breh. Too bad you don't have real lettuce. That would be so much more bro.
Brad: I know brah. All those Polo hats i wear destroy my flow. Guess I just have to settle for the sweattuce.
Troy: Word. Care to lax, bro?