How long is a piece of string?
The canonical example of an unanswerable question. The phrase is most often used as a scathing retort to a ridiculous query, for example:
Boss: How long will it take you to install the new software on all our servers?
Cynical employee: (snorts) How long is a piece of string?
Responding in this way implies that both questions are equally stupid, since the chances of accurately answer
ing either are equally slim.