That's terrible! What would I think? I would be angry and embarrassed. What would I do? Well, I hope I would have the courage and confidence to ignore them and get a great workout. If there are evaluations at the end of class, I would comment on the lack of welcoming atmosphere. But knowing me, it is equally likely that I would be discouraged and drop out of the class. If that is your choice, please let the management know why. And then find a better workout.