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