A poorly grown or awful looking mustache on someone who has no reason to have one, so therefore it can be assumed that their purpose in having it is to assist in the task of catching jizz so it doesn't enter their mouth after they have performed the act of oral sex. Also can be called a "JC" for short.
Friend 1: Hey Ian, that mustache is both terrible looking and completely unnecessary, why would you sacrifice your looks and integrity to have it?
Friend 2: It's obviously so I can catch jizz so it doesn't end up in my mouth after I suck some dick idiot, they call it a jizz catcher, try and keep up homo.
Friend 1: Man check out the jizz catcher that Carlos is growing!
Friend 2: Yeah man that's crazy, I hear they are really efficient though.
Friend 1: Efficient for what?
Friend 2: Catching jizz after oral sex do it doesn't get in your mouth!
Friend1: Oh ok, makes perfect sense now.