To have made a massive, catastrophic blunder. An extension of the more common "screwed the pooch," which adds a more severe consequence to the metaphorical action.
Since invading Iraq, President Bush and his advisors have really screwed the pooch and knocked it up.
The hypothetical man (often a sinistercharacter who decided not to go to boot camp) that is doing your girlfriend/wife while you are on deployment overseas.
Ain't no use in goin home,
Jody's got your girl and gone.
Ain't no use in goin back,
Jody's got your Cadillac,
Ain't no use in feeling blue,
Jody's took your checkbook too.