Perhaps he should wash more

Barack Obama: Now Senator McCain suggests that somehow, you know, I'm green behind the ears and I'm just spouting off and he's somber and responsible.
John McCain:: Thank you very much.

McCain could have responded with a bit more of a chide. Something like 'No. I never said that. I said you're wet behind the ears,' as that's the typical saying.

This is a blend. Not so much a syntactic blend, which ends up making a sentence ungrammatical, but a blended idiom. Obama took two idioms, the phrase wet behind the ears and the single word green meaning inexperienced, and combined them by replacing the adjective in the phrase with the single word -- easy to do because it's also an adjective.

Years ago in high school I wrote a story that I thought was very clever, about matador who won a bullfight then feasted on steak made from the slaughtered animal. He ate too much and got sick. He learned his lesson. Because of course the moral of the story is...