Defn of slang "Plank": Idiot. There is no slang usage of "planker". Take a closer look at your PCsearch. I'm guessing that your search engine (e.g. Google) converted the search to "plonk". Big difference. So, jetmech, be careful with the PC slang cautions.

I asked a guy if he was a Duc(ati) guy. He was fine until he found a city slang definition for a duc guy - no upper case. Too much information.