When referring to the districts of a city, the slums of the city is dirtier or more offensive than other districts involved.
S: "what would a BIG city look like in about a hundred years?"
B: "bigger"
A: "taller definitely"
S: "yeah.. taller."
S: "more metallic?"
A: yes, shiny is good, and the slums would be slummier... haha slummier..
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?"