(-noun -abbreviation)
stg stands for 'small tits girl'. Generally used to describe a female person (or virtual character) with small-sized breasts.
The abbreviation can (relatively)
safely be used among friends in public places, without raising
suspicion of the person in question.
(First seen being used in source-code of some game as a reference to a female
npc)
person A: Hey, you see that stg at
3 o'clock?
person B: That blonde?
Yeah, so?
Person A: She's cute!
Person B: Dude... why do you always go mental about
planks?