Not so much a bad line as a bad delivery, really. In 'Day of the Dead', the helicopter pilot is rebelling against the evil (well, not so much evil as cracking under the pressure) soldiers. One of them pulls a gun on him, but the leader realizes that the helicopter pilot is the only one who can fly them out of there, and stills his men with the command, "Wait. We need his ass."
Unfortunately, he doesn't say, "We need his ass," suggesting that they can't do without him and have to keep him alive. No, he says, "We need his ass," suggesting that perhaps the remaining body parts are expendable, but that fine ass of his is just too important to lose.
It's not much surprise that the pilot makes a run for it, really.