Huge list of ways to taunt telemarketers.
"I'm very interested in your program. But before I commit to buy, I need one more assurance. Can you guarantee me, in writing, that if I'm not 100% satisfied, you'll kill yourself?"
(shocked response from telemarketer)
"Look, you're asking me to risk my hard-earned money on this, based on your word alone, right? So I think you should stake your life on your claims. If your product isn't everything you say it is, I want you to kill yourself. Could you come out to my house and do it in front of me?"