Oh My Absent Fucking God. It's OMG but for Atheists. Technically you could use OMAG to be polite but nobody ever does; Atheists are angry fuckers at the best of times.
What? The rapture has been moved to 2012? OMAFG those Christians are stupid motherfuckers.
Oh My Actual Fucking God
An even more dramatic version to the "omfg" acronym.
omafg.. You don't listen to that shit...?