Any kind of cold calling really pisses me off, especially since they typically call when I'm in the middle of changing a diaper The use of machines to call people is especially annoying since I can't talk back. If it's a person calling I usually go with what dicksbro suggested and tell them that on principle I never buy (information or tangible goods) from anyone calling me or knocking at the door.

There's a super revenge to a cold caller on youtube if anyone needs a smile http://www.youtube.com/watch?v=J5z4Vs26-TI Maybe not altogether fair on the poor guy who rang, but funny anyway