Agreeing with a remark made at someone else's expense?

You know that moment when the only time your a** hole boss is actually being nice is when he's making a nasty joke about someone else; and you laugh or agree with it?? Be honest, did something equivalent of this ever happen to you? 

I'm only now just about able within myself to not agree with such a person when something like this happens. It's quite a bit harder than what you think when it actually happens... to be able to not agree and instead leave an awkward silence. In such a moment you can be fooled into thinking that your boss wouldn't say something 10 times worse about you to the very same person he's mocking.

I actually happened to remember a scene on TV recently which reminded me of this. For those of you who are familiar with 'Mad Men', it was when Don Draper found Roger's diary and started laughing at what he saw written to Peggy. But Peggy did not join in, and instead corrected him.

Of course it's not always going to be a boss who does this. But it's amazing the amount of people who are only too happy to sacrifice what they believe in and join in mocking another person, so that they can be down with the cool fella.