A Dirty Teen Mustache is a mustache that some teenagers thinks looks cool on them, but it doesn't. It's like the kid isn't meant to have a mustache, but he has one anyway. That's called a dirty teen mustache.
bawb: Hey, what's up with the mustache?
John: Oh, right, how's it look :D.
bawb: uh, no. Shave that Dirty Teen Mustache off.
Always on a Female, it's when she first notices small bit of fluff on her upper lip, she then shaves it off- not knowing that for life she is going to have a dirty moustache. She will then try to cover it up with some cheap poundshop makeup.
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.
FRIEND A: "Did you just take a stealthie of me?"
FRIEND B (turning phone around): "no I was just using snapchat's new filter, see?"