I was introduced to Andrew Wiles in a pub in Manchester during some conference.

It was immediately apparent that Wiles was reserved, shy and not in posession of a great deal of small talk. There was a pause in the conversation. The pause turned to a gap, then a gaping chasm. Oh my God! Must...say...something. Abruptly I blurted out

So tell me Andrew, what are you working on at the moment?
Immediately I realised that this was the dumbest question I could possibly of asked. Think about it. Here is man who has just spent seven years, that's right seven (count 'em), in conditions of total secrecy working on Fermat's Last Theorem. He told no-one what he was doing. This guy does not have any kind of a track record for blabbing out what he's working on to any casual acquaintance.

Wiles didn't answer me, he just smiled enigmatically.

See also Dumbest questions you've ever been asked.