Pardon my rant, but I've found myself to have less tolerance for stupidity and inconsiderateness. My wife says I've gotten much worse about it (sorry, babe).

1. Do not use things without permission of their owner.
2. Do not touch other people's musical instruments without permission.
3. If, for some unknown religious reason, you must touch musical instruments without permission, do not play said instrument or change the tuning of said instrument (no matter how "right" you think you are).
4. Do not touch someone else's computer without permission.
5. If, for some reason, you must touch said computer - leave it in the condition you saw it. And for heavens sake, whatever you adjust, put back to the original setting.
6. If you do not like the position of an object that does not belong to you.. tough.