Safe, Sane, and Consensual.
I feel that a good rule of thumb is that nothing is too hard or too soft to be considered BDSM. All that BDSM requires is some element of power exchange and the guidelines of “Safe, Sane, and Consensual”. This can be anything from a pair of handcuffs or just the idea of power exchange all the way to long recovery times or even permanent marking. As long as safety is taken into account and everyone is having a good time, how is another to say it is wrong? The question of what is enjoyable to watch is, however, a different question, and varies greatly from person to person and group to group. It is impossible to please everyone; one can only try to please the majority, and clubs cater to a diverse group of people, so some will enjoy something, and others will not and might complain. My only real advice would be to try to measure the crowd and do the best one can.