I would like to know if you have a boss and he is really in a bad mood, how do you handle this?

I have always had bosses.
And had incredible good times with most of them, but had few frustrations with few others I must say.
You got to be pacient when things don’t go well. Put yourself on your bosses shoes to understand his point of view.
And breathe.
We’re only humans afterall, bosses included.

To answer this question I have to put myself in your boss's shoes and think from his perspective. Whenever I am I a bad mood I tend to take it out on others without reason or, no fault of theirs at all. I can be downright rude and seem malicious to others and would not prefer to be disturbed during such an episode. After my mood turns back to normal I realize what a moron I had been and feel downright bad about it and try to make amends by being cordial to the individual's on whom I might have taken out on my frustrations on. My personal feeling is that you can not say "Sorry" and apologize enough to the individual when you have already hurt their feelings. I hope that answers your question.