Tell them to talk VERY SLOWLY, because you want to write EVERY WORD down.
Insist that the caller is really your buddy Leon, playing a joke. "Come on Leon, cut it out! Seriously, Leon, how's your momma?"
Tell the telemarketer you are busy at the moment and ask them if they will give you their HOME phone number so you can call them back. When the telemarketer explains that they cannot give out their HOME number, you say "I guess you don't wantanyone bothering you at home, right?" The telemarketer will agree and you say, "Now you know how I feel!"
After the telemarketer gives their spiel, ask him/her to marry you. When they get all flustered, tell them that you could not just give your credit card number to a complete stranger.
Tell the telemarketer you are on "home incarceration" and ask if they could bring you a case of beer and some chips.
If they want to loan you money, tell them you just filed for bankruptcy and you could sure use some money.
If MCI calls trying to get you to sign up for the Family and Friends plan, reply, in as SINISTER a voice as you can, "I don't have any friends... would you be my friend?"
Cry out in surprise, "Judy! Is that you? Oh my God! Judy, how have you been?" Hopefully, this will give Judy a few brief moments of pause as she tries to figure out where the hell she could know you from.
If they say they're John Doe from XYZ Company, ask them to spell their name. Then ask them to spell the company name. Then ask them where it is located. Continue asking them personal questions or questions about their company for as long as necessary.
When they ask "How are you today?" Tell them! "I'm so glad youasked because no one these days seems to care, and I have all these problems; my arthritis is acting up, my eyelashes are sore, my dog just died..."