It's good to smile every once in a while. The people that made fun of you back in school are long gone from you now. One of the things I regret was when people kept telling me to smile, I never actually done it... Now I almost have a reason not to, or at least to suppress it if I wanted to smile or laugh around people.
Once when I was volunteering at a soup kitchen since service hours were required for graduation, a man came up to me with his wheelchair and he had no legs. He looked at me and smiled, saying to smile since things could be worse, and then went. I wish I took his advice. Things could be worse. So take time to lighten up and smile around the people you care about and make some good memories, hopefully one day to suppress the bad ones.