Collective body shaming does NOT drive positive personal connection.
First of all, when you engage, you are being cruel to your body. Whether or not you are happy with your body's current state of affairs, publicly shaming it does no good.
Second of all, when you engage, the other person is FAR more likely to make the connection that future instances of collective body shaming are possible with you. This, in turn, precipitates further body shaming.
Third of all, avoiding engagement will slowly begin to turn the dial in your brain away from a future impulse to shame your body.
So, the moral of the story is if you are on the receiving end, don't engage. If you are on the delivering end, resist the urge and come up with something more positive to say.