This was first slurred by a drunken soldier in a bar in europe who was pinning over his impending divorce. The phrase was picked up by the soldier's friend who in turn made it his "catch phrase". It quickly gained popularity and propigated through out the military community. Within two years the phrase started showing up back in the United States.
The blasted soldier was trying to say: I'm stuck over here and she is back home. She met someone else. I'm over here. This is how this kind of shit happens, because he was blaming the military for shipping him overseas.
What came out of the soldier was: ah'm shruck ova heer an shees back home. Sheez met summ one cuz ah'm ova here. An thatz, Shit happens.