screw the pooch. Really screw up. In aviation, to screw the pooch is to die while failing to pilot an aircraft.

In Tom Wolfe's The Right Stuff, he reports it as slang used by test pilots in the California desert during the '50s, as jet fighter aircraft were being developed and tested. The pilot who “screwed the pooch” was the one who screwed up, often one who died in the wreckage of his plane. Wikipedia cites the origin as:

...first documented in the early “Mercury” days of the US space program. It came there from a Yale graduate named John Rawlings who helped design the astronauts' space suits. The phrase is actually a bastardisation of an earlier, more vulgar and direct term which was slang for doing something very much the wrong way, as in “you are fucking the dog!” At Yale a friend of Rawlings', the radio DJ Jack May (a.k.a. “Candied Yam Jackson”) amended this term to “screwing the pooch” which was simultaneously less vulgar and more pleasing to the ear.

The phrase took on a more general meaning after it appeared in the film True Lies. The main character and his team of spies had mishandled an operation; Charleton Heston's character—the team's chief—rebukes them by saying “we really screwed the pooch on that one.”