When someone is bragging about something, G4U is used so you don't have to say, "good for you," which can make it sound like you don't care depending on the situation.
Bob: I got 100% on my test!
by BJM February 21, 2005
A sarcastic way of congratulating someone.
Joe: I got an A+ in math. :D
by Fr3nch fr13s May 20, 2014