A mustache that a pedofile would have. It is unkempt and awkwardly unmanly. Often there is barely even any hair there and it looks like a sad attempt of a pre-puberty teen to have facial hair. Imagine Napoleon Dynamite's brother's stache but worse.
Johnny: "Hey, do you like the new mustache I'm growing?!"
Nathan: "Eww, no!! Shave that pedo stache off!!"
Robert: "Yea, John, shave that shit off; I have more hair on my ass than you do above your lip!!"