[PUGACHEV]

Whenever I answer robocalls — and I seldom do — I always just shout “What?” repeatedly. The person on the other end always shouts back “Can you hear me?” louder and louder until they hang up. It’s actually amusing to hear their frustration.

[Ahithophel]

Whenever I answer robocalls — and I seldom do — I always just shout “What?” repeatedly.

Good one. Another is "What's your name?" wait for the answer, rinse repeat and enjoy caller's decision to hang up.