I had a cold caller a couple of years ago who was working for a prostate cancer charity. He was hoping to sell me some advertising space on, if I remember correctly, some medical centre's appointment cards. He had got my number out of a small local business/tradespeople's booklet that I advertised in at that time. At that moment, I really didn't want or need to fork out any more advertising, and politely told him so. Rather than accepting what he said, he wanted me to explain why not, which of course I wasn't prepared to do. In the end, when he ended the call, he said quite rudely, "well thank you - for nothing!"
Two days later DH took a call and I knew before he handed it over to me that it was the same person. He was now going through all the numbers in a neighbouring area's edition of the same booklet in which I had the same advert.
It felt really good to let him go through all his prepared speech then give him a piece of my mind!