Dr. Goodman suggests trying to get 15 laughs a day, even if you have to look for the humor. It just seems about right to me. If you manage to reach your humor quota, you're probably feeling pretty good about life. Even if you don't particularly feel like laughing, try it once in a while anyway. The reflexes, the smile and the physiological changes your body will undergo just might make you feel better.
Laughter can be contagious, but so can the plague.
If you start making racist or ethnic jokes, people will start avoiding you. And never single someone out. Draw the line. Not everything is funny. And humor won't solve every dilemma.