Acronym; commonly extrapolated as "oh my fucking dog."
A term coined by the founders of the Church of Dog in the modern age of acceptability. It is often used by people whom hold dogs in higher regards than the mysterious, albeit conveniently absent figure that is God.
Users of this phrase commonly find little comfort in religion and the realm of spirituality, so they choose to modify the commonly used acronym "OMFG" in order to meet their standards of disbelief or arbsurdism.
Keren: *sends picture of adorable husky*
Max: "Sweet lion of Zion she's so precious!"
*immediately reciprocates with picture of cute lab mix*
Keren: "OMFD she's such a little bloop"
OMFD stands for "oh my fucking dick", although the d letter can mean something else. It was invented by some random newbie saberist in JK2 and used a lot by more random newbies such as gunners.