WHat you say when you've done something stupid. This expression catches peoples attention and should not be used in a professional environment. In the right scenario, it can illict laughter. Also used when you've forgotten something important.
For extra effect say: oh my god i forgot to microwave the baby
Dave: Hey Jim, did you remember everthing?
Jim: Umm, i think so- OH MY GOD I MICROWAVED THE BABY!
Shawn: I think thats everything... i packed clothes, locked the door, gave a key to the neighbors...
Brenda: Are you forgetting something
Shawn: *PAUSES* OH MY GOD I FORGOT TO MICROWAVE THE BABY!