Just because someone else is in a bad mood, don't let it change your mood. While it is very easy to take on someone else's problems, angst, or challenges. Don't you catch it!
Moods can be quite contagious. Unlike yawning, you can decide whether or not you're going to allow the bad mood of another dampen your day.
If you feel your mood shifting or changing in response to negative stimuli, shake it off! Make a conscious choice to maintain a positive and uplifting attitude.
Positivity trumps negativity any day, but you have to channel the energy. Rather than allowing a bad mood to infect you, enable your good mood to become infections to others.