Give One's Head A Shake Meaning

(idiomatic, Canada) To reassess the common sense of one's behaviour, ideas, etc.

Example: 2009, Joanne Chianello, "New program asks you to pass on the sodium", The Windsor Star, 20 August 2009:
  If you're thinking about topping your burger with ketchup, mustard, relish and perhaps a couple of pickle slices, you might want to "give your head a shake."
2011, Roxanne Hooper, "Please, keep the wilderness wild", The Record (New Westminster, British Columbia), 19 August 2011:
  But give your head a shake, people. Stop pushing for Wi-Fi at campgrounds around B.C. The entire premise of going camping is to escape from the hustle and bustle of our busy lives.
2011, Cam Cole, "Leafs lying scandal blown out of proportion", National Post, 5 December 2011:
  Talk about focussing on the unimportant. Give your head a shake, Google.
For more examples of usage of this term, see Citations:give one's head a shake.