This is an alteration of the internet phrase "WTG", which means simply "Way to go." The source of this is likely a not-very-well known educational videogame for the Phillips CD-I system on dinosaurs. The narrator/main character would say that phrase when you were successful in the game. It's also possible it stemmed from the common use of the phrase "rocket science" in comparision to difficult activities.
It can be used sincerely, though it is more often used with sarcasm.
Person #1: I was late for work and got yelled at by the boss.
Person #2: Brilliant. WTGRS
EXAMPLE 2 (Sincere)
Person #1: Wow! I just won the lottery today!
PErson #2: WTGRS!
Christian: errr no who won?
Sam: Im not sure i was asking you because i thought you would know?