Write an article based on this "Validate how they are feeling. Avoid confronting them. Try flattery. Use humor. Look for the underlying cause."
Don't try to minimize their feelings or tell them that they should "just get over it." Doing this will only make them more upset. Instead, try to validate how they are feeling. Try saying something like, "I can tell that you are feeling upset. What's going on?" The last thing a person in a bad mood wants is to be confronted. Instead of helping the situation, it will only add fuel to the fire. If you must get to the bottom of the problem, you can do it in a gentle way. Let's say your friend has been in a funk for a whole week. Instead of saying, "Why are you acting like this," you could say, "I really want to understand what's going on." This comes off as less defensive. Your friend still may not want to talk about it, but you likely won't have upset them even more. Hearing nice things about yourself is often an instant mood-lifter. Saying something nice to the person who is in a bad mood may lift them out of their funk. It can also help bring you closer together during this unhappy time. You can thank the person for helping you earlier in the day or compliment them on their appearance to try to help them feel happier. This nice gesture may help them snap out of it. Tell your partner "I really appreciated you coming to my event last night. I know you have been stressed with the upcoming deadline. It means a lot that you took time out to support me." You can also invite them to do something they might enjoy, such as going for a walk or playing a game. You may be able to end the bad mood by having fun with it. The type of humor you use depends on the person's personality. If, however, you know that humor won't work well with this person, then you should probably avoid it. For instance, your coworker storms through the office after a bad performance review. It may not be a good idea to say "Who lit a fire under you?" jokingly. However, if your coworker spilled coffee on the briefings and got really upset, it may be well-timed to say, "You have just used your last screw-up for the week. Please refill your "screw-up" card now for more credits." Sometimes what seems to be the cause of the bad mood isn't actually what's really going on. Try and take a step back from the situation and attempt to determine what could be the problem. Perhaps the person has a headache, is having a bad time at home, couldn't sleep the night before, or just found out they have a serious condition. These problems could contribute to the bad mood that you've walked in on.