If your best friend kept insulting the guy you like every time you talk to him, walk pass him, look at him or when you talk about him. What can you do? I know she's my best friend but I don't think she should keep insulting him? HOW?

Be honest, tell her "actually I think he's quite nice" if she carries on then she's not much of a friend and a friend you can do without.

Tell her she's being childish and should not speak badly of someone she doesn't know and probably never will know, and ask her would she like it if someone did that in regards to her.

Or you could just ignore her, shell soon get tired of it once she realises you aren't bothered, its possibly because it bothers you she does it.

It's a childish thing to do though..

Basically she is attention seeking, so don't give her what she wants attention...

If your friend cannot stop her behavior just because you asked her too, not much of a friend. Talk to her.