Reverso-phones

Most headphones leak some sound into the surroundings. Reverso-phones leak out the exact opposite type of music to that which you are secretly enjoying.

They do this because they have a small set of extra tiny speakers that deliver the "leakage sounds" of Mozart, whilst the main ones are blaring the otherwise embarassing rantings of Megadeath (or similar) directly into your ears.

Of course progressive youthful listeners can reverse this effect to work the other way round.

note - title may change as I think about this during the day.