Here's an idea. When you hear them knock, stand behind the door as you open it so they can't see you and, in the most Dracula like voice you can muster, say:
"Plllleeeeeaaaazzzee, Cooomme iinnnnn! ... I've beeeeen exPECTING YOuuuuuuuuu !" And just stand there behind the open door, remaining...