Pity we have to put up with this ort of harassment.
For the phone jerks I have used 'Hang on a minute, just have to turn the stove off' and never return....they usually hang up after 30 seconds but still keep ringing back.
The best one was 'Who are you? Do you realise you called an unlisted Federal Police Number? I need your name, contact details, and who authorised this call' by which time they have hung up and never call back.
With the door knockers, when living in a country town on the Darling Downs in Southern Qld about 27 years ago I couldn't help myself. The usual crowd turned up on a Saturday morning banging on about devil worshippers in our midst which led me to invite them inside to taste some of the goats head soup we were cooking up! The look of astonishment on their faces was priceless but probably not the best thing for one of the town's bank manager's to be telling this sort of stuff to potential customers however it was a good laugh at the time.