OMG

abbreviation

ˌō-ˌem-ˈjē 

variants or omg

oh my God

—used (as in email or text messages) to indicate that something is considered surprising, shocking, thrilling, etc.

Their harmless [email] chatter ("OMG! I was playing yesterday, when this really CUTE boy rode up on his bike") is reminiscent of the notes we used to pass in class …

—Janet Malcolm

—sometimes used as an interjection

Then she stopped in the middle of the aisle, snapped her fingers, and exclaimed, "Hey! Does he have Guitar Hero?" "No, but he has a Wii. OMG, you are a genius!"

—Jessica Hulett