an expression defining how stupid someone is; chiefly British.
i.e.: the thickness of two planks of wood stacked one atop the other.
sometimes shortened to "two short planks"
A piece of wood that you put up against your door handle to stop anyone coming in your room.
hey whats he doing with that plank of wood
i think he's gona use it to stop anybody going into his room whiles he's doing stuff, he calls it his wank plank