OK, here are some practical jokes to play on them
*Answer the door with a porno mag in your hand
*Answer the door in the nude
*Answer the door, when they ask a question just say "Hmmm, just let me get my gun"
*Answer the door dressed up like Jesus
*Don't open the door, but say in a loud booming voice that you are God, and if they don't leave soon, they will be sent to Afghanistan to be a sex toy for a frustrated pack of camels.
*Open the door and throw cutlery at them
*Open the door, have your eyes shut, and just start pissing on their shoes, then try and flush, then go back inside.
*Open the door and say "Hello, are you interested in joing my new cult?"
*Ask them very inappropriate questions after they have said something to you. for example "I heard if you rub rhinocerous semen in your scalp it will actually promote hair growth. Is this true?"
*Open the door, look in horror, start crying and screaming and yelling out "Make them go away, please make them go away, I can't deal with this mental torment any longer! I can't take it anymore, I can't live anymore!" then disappear to the kitchen and bang a pot on the bench, making a loud bang, and then shriek loudly.
*Open the door, put your hand out to shake their hand. When they grab your hand, lift it toward your mouth and bite them then say "mmmm tasty, tastes like crayons!" then try and bite them more.