A fork of Rural Dictionary
A futon in the apartment (usually studio) of a loser who has no girlfriend and is always masturbating.
Kristen: Whew, I thought I might get pregnant the other night. Jacinda: Why, what happened? Kristen: I sat on Santosh's cum-stained futon when I visited him.
A cum-stained futon (or CSF) is what you find in the home of a low-class loser who is always at home beating off on his futon. It is stained with his semen (cum) drops.
Jane: Did you visit Peter's apartment? Mary: Yes I did. He had a cum-stained futon in there. Jane: Yuck!