"ZOMG is a varient of the all-too-popular acronym "OMG", meaning "Oh My God". ZOMG originated from the imageboard 4chan.org and one of it's members Zardoz.
Always used in all-caps, 'ZOMG' is generally used in a sarcastic manner, more often than not a humiliating fasion. It is also used as a device for stating the obvious.
'ZOMG REI-CHAN!!!' - A 4Chan user exclaiming sarcastic joy over a picture of Rei from Evangelion."
Well, obviously, a big fat black guy dressed as Sailor Moon is pretty messed up. But so is any guy dressed up as Sailor Moon, regardless of skin color or body weight.