Do you think it's strange if I bring my adult son to a dinner with my friends?
No, why do you think it would be strange?
They're friends that I hate and I want my son to see that.
You shouldn't bring your kids to an event with people you don't like. It'll make things uncomfortable for everyone there. Your child may be upset that you put them in such a position.
I want to expose my friends for the frauds they are. This will teach my son to be careful about who he calls "friends" during his life.
This sounds like it would be an intense situation. If you want to teach your son about interactions like this it would be better to discuss your feelings about others with him one on one.