Back in the day, when companies tried to get you to switch long distance providers, I had a cold caller call just as I was heading out...

Cold caller: Hi. Would you like to save money on your long distance bills?

Me: No.

Cold caller: Ummmmm. Ohhh Kay...

Me: Bye

Took them out of their opening book in one move.

Check and mate.

I get a lot of door-to-door salesmen offering window replacements.

I just tell them "We're a Linux household, no interest in windows" and slam the door. I think the look of bewilderment is worth it.