If you do this, you'll get 7 years of bad luck

...break your mom's back

TRISKAIDEKAPHOBIA!

No whistling here

3 cigarrettes, one match?

Do this to keep the devil at bay

Do this and you'll destroy the sanctity of the trinity

In the dark ages, this poor thing was considered the "incarnation of Satan" thus it should die in a bonfire

Do this to to concentrate the forces of good spirits and to seal a pact or a wish with anyone.