Burn your bridges when you come to them?
What Is a Mixed Metaphor?
A mixed metaphor is when someone combines two unrelated metaphors. For example, two common metaphors someone can use to tell you to get a clue are “wake up and smell the coffee,” implying you need to be more alert, and “read the writing on the wall,” implying you need to see the bad news that is already right in front of you. A radio host once told me his favorite mixed metaphor combined those two. Someone told him to “Wake up and smell the coffee on the wall.” Suddenly the imagery doesn't make so much sense. Did someone throw coffee on the wall?
Sports metaphors tend to be popular and they're also easy to mix. For example, if you tried to motivate your co-workers by saying, “It's our turn at bat, so let's make this touchdown for the company,” you'd have mixed baseball and American football metaphors, and if you try to imagine the image that goes with the metaphor, you don't know whether to put your players on a baseball field or a football field.
Can Mixed Metaphors Be Fun?
Because they usually undermine the imagery of both of the metaphors that are combined, mixed metaphors are generally considered bad form. But sometimes people also like to play with mixed metaphors. It can be a fun way to turn a cliché on its head. For example, I've seen people mix the metaphors “Let's cross that bridge when we come to it,” meaning let's put off the decision, and “Don't burn your bridges” meaning don't destroy a something you'll need later. They get “We'll burn that bridge when we come to it,” which combines the meaning of the two metaphors into something like “We're ready to fight when the right time comes,” and still maintains imagery that makes sense.
Was Obama mixing metaphors with his “green behind the ears” statement?