It's an emoticon of a smiley face using a hat backwards
Example:
Person 1: q:)
Person 2: woah dude nice hat
the most useless letter in the english alphabet
why does q exist
Spanish slang for "Que", or "What". Has surpassed into English language. Mostly used as a passive-aggressive insult when someone does not read a whole message. Mostly used in texting apps.
A: Hello, I was wondering about your availability for working at urban dictionary.
B: q
"Q" shortening of Thank You, but can be used in awkward/funny moments by just saying "Q".