While I was telling my trainee how to fit her helmet, I got some help by a fellow cyclist. As the cyclist zoomed past it was not hard for me to show my trainee what not to do.
The cyclist had put the helmet on back to front.
Over at safekids they have made a video on how to fit your helmet correctly. Even though this website is made for kids, fitting a helmet is the same for adult and kids.
Remember : An ill fitted helmet is as good as no helmet.
LINK : http://www.safekids.co.uk