When the group chat starts roasting someone who isn’t in it, the one who changes the subject is the real friend.

A pile-on has its own momentum, and by the time you notice, nobody remembers who started it. Defending the person directly can turn the group on you, which is why most people stay quiet and feel bad about it afterwards. Changing the subject is a quieter tool and it works, because the energy needs feeding and you just stop feeding it.

Send something unrelated: a question, a photo, anything at all. Nobody will notice you did it on purpose. The person who eventually finds out the chat existed will.