1. Do not urinate in the elevator. It may seem like a convenient, private location, but the entrance-way to the building is usually better ventilated.
2. Do not cast objects over five pounds of weight into the elevator shaft. Although the shaft is very deep and has space for a large amount of trash, heavy objects could penetrate the roof of the elevator, causing hurt to passengers inside. This rule does not apply if you are certain that the elevator car is on a floor above you.
3. While forcing your way into the elevator, it is polite to excuse yourself when you need to push others by the arms and shoulders and buttocks. While entering, if you accidentally push people in the face or in the privates, a quick apology is in order.
4. On average-sized elevators (approx. 3 feet wide by 4 feet long) the passenger limit should generally be regarded as 6. It is not polite to force your way onto a 3 by 4 elevator if there are already six people on board.
5. While writing, drawing or spray-painting on the walls of elevator, make sure not to get any felt marker or paint on fellow passengers.
6. While the elevator is moving, avoid contact with the floors passing by the open door. A poorly placed arm or leg could quickly be torn off if caught between a floor and the elevator car.
7. Especially for new users: If the elevator car jerks strongly or free-falls for a meter or two, do not panic or scream. Locals find this behavior disruptive and irritating.
8. While smoking on the elevator, try not to blow smoke directly in other's faces, and try not to touch them with the burning end of your butt. Remember that it is safer to extinguish your finished cigarette on the floor of the elevator rather that to cast it down an elevator shaft and risk it making contact with unseen flammables.
9. If you are a non-smoker, do not grimace, wince or cough while others smoke in the elevator car. This is considered extremely rude and presumptuous by the locals.

Item compliments of Chris McGrath, retired web developer and bosnian resident. This certainly does help to put things in perspective, chris and gina are ever-reliable on that front.