It seems to me a HUGE part of social interaction is simply being able to superficially laugh along with the group. I - like virtually everyone - want to be loved and be part of the group, so I try to laugh along. When I'm not genuinely amused though (which is quite often), I have a smile that's downright painful. What do I do about it? Just having a neutral expression on my face, will result in me being regarded as humorless. That has happened in the past and being alone in a crowd.