I masturbate furiously while cutting myself and crying.
Not really.
For me, it's all about attitude. I don't want everyone around to be going 'Aw, he's sad and dissapointed', so I start acting like I'm not, crack a few jokes, and within twenty minutes I'm in an honestly positive attitude instead of acting like I am.
Seriously, there's only one reason you can sit around letting yourself feel upset about something, and that's because, for some reason, you want to feel upset about it, or you want others to know you do. I know it's hardly as easy as 'Be happy', but if you put yourself in the mood where you're open to a positive attitude, you'll get one.