I used to tell them that I had a brother who is recovering from a mental breakdown and the doctors said that he needed to start interacting with strangers again. A short pause to get crazy bro and I would start gibbering about how their product was a front for the moon men that come to visit every night. Also sometimes crazy bro needed written and verified proof that he was talking to an actual mammal, because their voice sure sounded reptilian. “How can I say yes when you might have been hatched from an egg?!!” and “I sympathize, but you must realize an actual reptile would also deny it.”
Freegards
Another one I did, was when my son was a toddler. He loved to talk on the phone, but you couldn’t understand a word he said. After getting a call from a telemarketer, I’d tell them to excuse me for a minute, then let my son talk to him.