It's just an expression we use to emphasise how little they no about something. You'd know something if it hit you in the face, or should, but these charmers are such hypocrites that if a principle hit them in the face, like a clown's cake, they wouldn't know it for what it was. It just serves to suggest that they are especially low forms of life. I don't know much about Canadian politics, but this is a decidedly spicy and no-holds-barred editorial. The paper is clearly challenging them.
Student or Learner