Can't stand door knockers.
Our door is glass, so if I turn the corner and see them, I just turn around without answering the door.
I'll never go with any organisation that tries to solicit me with a door knocker.
I never saw the guy until it was too late. Was oblivious out the back of the house as the wifey was yelling to nobody that someone was at the door. I walked around the side of the house carrying a hose and a shovel and here's this guy with a clipboard at the front door. Never had a chance to raise shields and arm phasers before he started up with his spiel. Took me about 5 minutes to shift him.