when 12 y/o boys start to grow their "mustaches" and think they are cool for not shaving them.
"the 12 y/o think he is the shit for having a trash stache, but when his mom told him to shave it he died on the inside for losing his man hood."
A poor excuse for a mustache, generally sported by: military personnel, awkward loser teenagers, trailer trash, rednecks, Mexicans/Latinos, and/or police officers. A trashstache is typically worn by men that lack the balls or coolness to wear a characterful mustache, i.e. handle bar, 70's pornstache, freak-show carnival announcer stache, Hitlerstache, 18th century safaristache.
I saw a poser gothic teenager at the mall today. He was wearing an Insane Clown Posse t-shirt, baggy hot topic pants, had a crew cut, and trashstache.
Military men trying not to look stupid with a high and tight or trying to blend in with society grow trashstaches.