A comment from this post on "How to deal with Crappy People".

A number of years ago I had a two part epiphany.
 
1. Since I already knew the world had plenty of assholes, there was no reason for me to be surprised, angry or upset when my path crossed one.

2. When someone appears to be an asshole one of two things is going on:

• First, this may simply be a good person having a bad day. If so, they don’t need me in their face.
• Or, this could be a genuine asshole who needs a can ‘o whoop-ass opened up on ‘em. But I don’t have to do it. They will come across another asshole and serve each other. Not my job.  

Simply understanding these two things has greatly enhanced my peace.