McBlumpkin Decker Share definition Flag When you get a blumpkin while leaving an upper decker in the rest room of the golden arches. Get theirs to go... They've been in the bathroom long enough to leave a McBlumpkin Decker. McBlumpkin Decker by ronald mcBlumpkee January 4, 2010 0 0 Get merch Get the McBlumpkin Decker mug. Buy Now — $32.95 See more merch