Hate is such a strong word and such a visceral emotion. Are we really talking about HATE here or just dislike or disrespect for my opinions or lifestyle?
If someone HATED me, I would probably know it pretty quickly - I have a well-tuned BS monitor. If they DISLIKE me, then I'm with some of the other posters here - whether I want to know it or not depends on the situation.
For instance, when I meet with clients, they may not like my advice. They may not like my haircut. They may not like it when I tell them that the error is their's and not the bank's. But frankly, I don't care. I'd prefer they be civil in that context, just as I will be polite and kind toward them, even if inwardly I'm screaming, "You are a freaking idiot!!!!!"
Same with a co-worker - I prefer a polite and respectful workplace, even if it means we can't be brutally honest with each other. What's the point of making everything personal? There are ways to be honest about OPINIONS and IDEAS, POLICY and PROCEDURE without making such topics a personal slam.
I think that the route one takes in those situations is an indicator of maturity level.
As for friends and family - usually if someone is twofaced, it becomes apparent pretty quickly. I doubt that I would be able to change that trait in them. So I guess whether or not I call them out on it depends on whether or not it would make a significant difference for the better in anyone's life or situation.
If not, then I just let it slide and avoid getting my emotions tangled up in their personal drama.
Southerners call this GOOD MANNERS by the way.