"Men are disturbed, not by things, but by the principles and notions which they form concerning things."
~The Enchiridion
This is the basis of Stoic ethical philosophy.
This is also an innate feeling many of us realise as children.
Deep High School philosophy right? Well.... We may figure it out then, but for some reason, we forget it.
Are we dismissing it as false? Childhood stupidity? I have no idea, but I've known this since the 8th grade.
Some like to say "it takes two to tango" or some other silly platitude, but the reality is, it only takes one.
I could sit on a couch and be offended. I could be out at a bar and someone calmly insults me in a language I don't understand, and I may be confused, but likely not offended.
Now, if that same person said those insults to someone who understands him, that person may believe that the insulter is also the offender.
But he is wrong, for if he was the offender, I too would necessisarly have been offended.
Therefore, we only offend ourselves.
My reactions are not caused due to your actions. They may encourage me or attempt to incite me, but any offense I may have is my own doing.