Surely everyone has extra friends outside of their group. But it sucks when one of your friends is also friends with someone you hate! Here are some tips on how to deal with it.
[edit] Steps

1. Accept it. Your friend hangs out with someone you hate, that doesnt mean it's the end of the world.
2. Talk to your friend about that person, BUT NOT IN A BAD WAY. Just tell them that you're not a big fan of their other friend in the best way possible, without being mean.
3. Don't talk about the person you hate behind their back. It's mean and will make YOU look like the bad guy.
4. Be happy, confident and fun to be around, that way your friend will favour you over the other friend that you hate.
5. No matter how mean the other person is to you, or how much they talk about you, keep your lips seeled.
6. Even though you hate them, try to like them the slightest little bit. Negativity is bad for all three of you so try to be civil.
7. Try to be aquaintances with that person-auaintances that don't kill each other


[edit] Tips

* Try to keep your friend aware of your feud or beef with the other person so that they dont end up inviting them over when you say "you can bring another friend," etc.
* Try to avoid being around the person you hate.
* Don't be a jerk about the situation, for example your friend says "me and [person you hate] are going to see a movie, you want to come?" Shrug your shoulders and go anyway
* If you are nice, fun to be with and hang out with your friend alot, they will most likely like you better and eventually lose contact with the person you hate.
* You can end up "stealing" your friend away from the haters.


[edit] Warnings

* When your friend invites you somewhere with the person you hate, only go sometimes or he/she will think you and the person are becoming friends



Source:http://www.wikihow.com/Cope-With-a-Friend-That-Is-Also-Friends-With-Someone-That-You-Hate