Interesting fact:

“OMG!” This slang term sounds quite modern, but the first recorded use of this phrase goes all the way back to 1917 when Lord Fisher started a letter with it to Winston Churchill. "I hear that a new order of Knighthood is on the tapis – O.M.G. (Oh! My God!)” He made sure to write it out in full next to the abbreviation, somewhat destroying the magic.