A Twelfie is name of the act where a twelve-year-old takes a selfie and uploads it on social media.
My feed is full of fucking twelfies!
The act of estimating the cup size of a female, or considerably more rarely, a male.
Person One: "Dude, she's rocking a D-Cup."
Person Two: "For Real?"
Person One: "Nah, I'm just having a breastimate."