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

Writing as if he were Sonny, Hamish joked: "OMG, I lifted my weight in kilos …"

—Stephen Milton