Defend your friend when they’re not in the room. That’s where loyalty actually lives.

Loyalty gets measured in the rooms your friend is not standing in. Agreeing with someone to their face costs nothing, while saying something when a group is warming up to talk about them costs a little social standing, which is exactly why it counts. People who only defend you in person are not really defending you.

You do not need a speech for this. A plain line ends most of it: that is not fair, or I know them, it is not like that. Then change the subject, because the goal is stopping it rather than winning it.