Well there was the time when my ex-mother in law had bought a set of crockery at an auction which was promoted as being unbreakable. She came home all excited and invited us all to watch.

"Look - these plates are unbreakable!" she said triumphantly, holding one above the quarry tile floor. Then she let go.

It didn't just break - it exploded! It took her a long time to live that one down. She died a few years ago, but even now, 30 odd years later, someone only has to say "Remember the unbreakable plates.......?"