humor in the workplace

it's quite common to read advice about encouraging managers to introduce some humor into the workplace.  however, it's also apparently true that one of the most stressful aspects of subordinates' jobs is not knowing how to react to their manager's humor.  dash9 makes it easy for subordinates by demanding that they laugh at all of his jokes.  and he never clarifies when he is joking.  what's the reaction for laughing at the wrong time?  note the previous post about morale and beatings.