A bad mood kept to yourself is just weather. A bad mood you aim at people is a mess somebody else has to clean up.

A bad mood is not a moral failure, and nobody chooses the weather in their own head. What you do choose is whether other people have to stand in it. Aiming it at someone turns your rough afternoon into their problem, and they will remember being snapped at long after you forget why.

Containing a mood is not the same as faking a good one. You can say plainly that you are in a foul mood and it is not about them, then take twenty minutes alone. That sentence costs nothing and saves somebody an evening of wondering.