Bitching session

It seems lately that the only to show empathy towards my co-workers at work is to join in the bitching sessions and sometimes I am not in the mood. You have to be quick, rude, bold, loud and if you can be funny even better when it comes to making negative comments, I don't want to cross that line sometimes because I feel that it will interfere with my productivity and work ethics. Where would the bitching session be without character assasination of another employee sometimes I cannot join in because I feel things will come back to hunt me. I try to give everybody a couple of breaks at least three, before jumping in the negative band wagon. Do to the fact that I am constantly changing jobs, I try to maintain a level of professional boundaries.