My girls lining up to kiss me in the morning before I go to work. That makes me smile everytime. Especially that 3 year old and the look on her face when she does it. Ok outside of the pathetic romantic stuff, I would say that putting words into peoples mouths with a friend while watching them talk is about the funniest shit I can think of.
when I am in a good mood I smile at everything just about. so it would be my mood. and the muscles in my face have a lot to do with it.
I smile when I'm nervous. Hmmm my friends make me smile, as well as my family and my dog. I smile all the time really.