It is a question of intention. You can smile with an intention to offend, then smiling becomes a sin. Anything can become a sin if deep down the desire is to do violence. And anything can become virtue if deep down there is a desire to create more joy in life, more laughter in life.
My own understanding is that there is nothing more valuable than laughter. Laughter brings you closest to prayer. In fact only laughter is left in you when you are total. In everything else you remain partial, even in lovemaking you remain partial. But when you have a really heartfelt belly laugh, all the parts of your being -- the physiological, the psychological, the spiritual -- they all vibrate in one single tune, they all vibrate in harmony.
Hence, laughter relaxes. And relaxation is spiritual. Laughter brings you to the earth, brings you down from your stupid ideas of being holier-than-thou. Laughter brings you to reality as it is. The world is a play of God, a cosmic joke. And unless you understand it as a cosmic joke you will never be able to understand the ultimate mystery.
I am all for jokes, I am all for laughter.