EG, sitting on stone steps gives you piles, going out with wet hair will give you a cold, too much sugar in your tea gives you worms, any red food is good when you are on your period, watching TV too much makes your eyes go square, milk goes DIRECTLY to your bones and teeth to make them stronger, standing on your head makes you cleverer, swimming after food is deadly, chocolate gives you spots...
Any more for any more?
(Shamelessy derived from the expressions thread :) )