I teach, engineers and construction workers. They are always on the look-out for something to take the rise out of, but are fortunately too quick on the draw to look closely.

In other words, they spot the long nails on my left hand and ask the question (usually just "why have you got long nails?" but occasionally "are you a transvestite, then?") and I show them the other hand and ask what the hell they are talking about!

If I spot people noticing who might be too polite to ask, a little "air Segovia" usually lets them know why. Other musicians tend to twig fastest - some even work out I'm left handed - and I've had a couple of music-related discussions or jam sessions grow out of that, one even at a job interview!

People's perceptions say more about themselves than about you, and pointing that out is far more effective than the middle finger, I have found.