If it's someone else in a bad mood, try singing to them.
It was worth a shot.
Lifehacker has ten persuasive suggestions for how to handle things when it's you in the mean reds and I rather like the last one:
Lastly, while it may seem counterintuitive, you may have to spend some time on what's bothering you. If it's something you need to deal with, pushing it down isn't going to help. Instead, think through what's making you mad—whether it's a piece of bad news or something else—and let your brain fully process it. If you do, you can actually lessen the effect it has on you. That isn't to say you should dwell on it all day long, but if it's something you need to work through, you're better off doing it now than letting it fester.P