A major cause for loads of Sin'as Chinam is that you feel that the other person looks down at you and thinks he owns the world. “Only WE have the right Derech, and only OUR leader is the real thing”. If it’s true that these people really think they’re on top of you, then they have much worse problems than you do.
תוֹעֲבַת ה' כָל גְּבַהּ לֵב משלי טז ה A haughty person is detested by Hashem, and Chazal say they are first class Gehinom material. You may be the official nebach of the universe, with very little Torah and Ma'asim Tovim, and plenty of all kinds of sins. But according to the Chovos Halvavos in Shaar HaK'niya, you are way ahead of them, despite their greatness in Torah, Avoda, and Gemilus Chasadim. (However, NOT trying to improve yourself is certainly not recommended).
People hate big shots! “Only we have the right Shita!” However, I strongly suspect that you simply don’t understand these people. They may have a desperate need to be on top, and they are actuality quite broken inside, just like you are. If you are always building yourself up and appreciate yourself fully, then you’ll laugh at their childish arrogance, and you’ll be Dan them L'kaf Zechus.
If you get closer to them it may be a totally different story. Lots of Sin'as Chinam comes from being ignorant of the true inside story of other people. Those who make an effort to understand people who are hard to swallow, are the true Bnei Aliya.
Novardok
Rabbi M. Zatzal was married to a woman who wasn’t well, physically and mentally. They say that the war affected her. I was once on the telephone with her, and I saw how weird she was. She was screaming and kvetching on the phone about something that bothered her, and she didn’t sound appropriate at all.
Yet, when Rabbi M. Zatzal (who was a Gadol B'torah) couldn’t figure out a Tosafos for a week, he blamed himself, since he had complained to his wife about the gefilte fish that she made. So he made up with his wife, and right afterwards the Tosafos became clear to him! He didn’t say “I'm married to a crazy lady and it’s all her fault”.
This Rabbi M. Zatzal once told me that there is nobody in a person’s life except himself and Hashem. People are all tests to make you great, some way or another (by doing Chesed with them, or by being Sovel (tolerating) them, etc.). When a Novardoker sits at his Shabbos table, his main goal is “not to fall into Ka'as”, more than singing Zemiros nicely and having everyone behave.
וְּלַעַנָוִים יִתֵן חֵן משלי ג לד The humble Anav has Chen. He’s soft, kind, and gentle... and he wins
