I know a guy with down syndrome (kid of my parents' friends) and I would have to say he is the happiest person I know. Anytime I see him, he gets a huge smile on his face. He walks over to me and asks me how I am doing. He is such a friendly and cheerful guy. I saw his mom scold him for being disruptive and he got a frown for like 10 seconds and then he returned to being the happiest guy around. To be able to always be that happy is a goal so many of us fail to achieve.