Just start speaking in your own language that you make up, or act like you fell asleep on the phone and start snoring, that's what I do. You could tell them that you doctor just gave you one week to live, that one works too.
Whenever I get telemarketer calls, I generally state right away that I am not interested. If they make even the slightest attempt to continue their pitch, I hang up. If, for whatever reason, they call back, I ask to speak to their manager and at least hope they get their ass chewed out.
