Ford 5150 Share definition Flag (n). Slang for Ford F-150 truck. 5150 is code for the criminally insane, which is what you may be if you drive this junk. Ooh boy there's a big bad Ford 5150 on the side of the road with the hood open. Ford 5150 by boggler January 28, 2019 0 0 Get merch Get the Ford 5150 mug. Buy Now — $32.95 See more merch