I got a telemarketing call so, on a whim, I said something like:
Hello. <long pause, then even if they are speaking, say>
You have reached a prototype virtual human using artificial intelligence. <pause - now they are listening. Then say>
With my speech recognition and speech synthesis software I am fully capable of conversing with a human. <pause>
What would you like to talk about? <pause>
<This should all be spoken slowly and deliberately.>
The guy covered the phone with his hand, asked someone something and then hung up. He must have bought it.
The trick is not to laugh and see how far you can take this. Do not stumble over any words!