When someone is in a bad mood, you give them space, or a lending ear, or a hug. Depends on what they need or want. But trying to cheer someone up when they're obviously dejected and have every right to be? Nah. I would never tell anyone to cheer up, smile, put on a fake mask. For me, it's the equivalent of, "Stop being so whiny, you're making me feel uncomfortable!" As if it isn't decent to show your true feelings in front of other people. Let people grieve, or rage, or whatever. That's the only way they'll heal.
So no, I don't like it when people try to "cheer me up", even if they don't tell me that explicitly. I feel very strongly about that phrase for some reason. When I'm in a bad mood, I just shut other people out until I know I won't lash out at them. Things could get very ugly when I'm too influenced by my own emotions. Space clears my head.