Martin,
The penalty would depend on the player involved, (based on history, experience, reputation, etc., etc.). Others may not agree with me but, there is a difference when action is heads up, and when there are multiple players. Exposing your hand when facing one player might be a tactical move to try to get a read, or reaction from your opponent. However, showing your hand, with action pending, against multiple players is a more serious violation of poker etiquette and warrants a stricter punishment.
I believe there are others that can give you a better range of punishment, than I.