I've had fun using this approach (I read about someone using it years ago, it works just as well today).
Telemarketer: Good evening sir, I'm Annoyo-man from Shoddy Remodelers. We're having a half-price sale on new CrystalClear windows this month and wanted to know if Tuesday at 7 PM would be a convenient time to have our consultant stop by to give you an estimate. Or would Wednesday at 8 PM be better for you?
Me: Tuesday at 7 would be great! Half-price windows, you say?
TM: Yes! This is our best price ever on these top-quality windows. That's great, I'll have our consultant stop by on Tuesday around 7 PM. Can I just confirm your address?
Me: Can he bring turnips?
TM: So, you're at 1313 Mockingbird...turnips?
Me: Yes, can he bring turnips?
TM: Uh, I'm sorry, I don't understand. Did you say "turnips"?
Me: Yes, I'd like him to bring some turnips.
TM: Uh...
Me: That figures! I had a guy here last week to estimate windows, but he wouldn't bring any turnips. He had to leave, so I'm still looking to get new windows.
TM: <click>
The best part is they obviously make some notation that you are a lunatic and will never call back.