a rail-thin mustache; usually on 26-45 year-old sex offenders who have finished puberty but by the looks of their 'stache, you would think that they just began puberty. they do not have to be sex offenders, but those who are not guilty of the crime tend to shave it off at the sight of the thinness above their lip
Person A: "Hey, look at that guy's mustache. He's old, but it's growing in a 13-year old's would."
Person B: "That pervert has a molester mustache"