Here's an easy guide way to guarantee someone will knock on your front door.
Step 1: Stand at the kitchen sinkWhether or not you answer is your call. If you DO, and the bad luck is countered with good luck, it will be someone trying to sell something.
Step 2: Half-fill the kettle and, deciding that the inside is "a bit gross" swirl the water around.
Step 3: Empty the water, but let your brain confuse you and aim the swirling mass of water at your genitals.
Step 4: Step back, look down - then hear someone knock on the door.
Man From Sky TV: "Afternoon sir, can I interest you -"Here's the money shot:
Me, cutting him off: "Sorry, can't chat, had an accident."
MfS, looking down: "Oh, er, um, OK sorry bye!"