It seems to me that tolerance for others is closely related to tolerance for ourselves. It we are compassionate and forgiving of ourselves, we tend to be the same way with others. If we are hypercritical and judgmental of ourselves, we tend to be the same way with others. That inner critic who criticizes everyone else is a reflection of the inner dialogue we are having with ourselves.
Learning to accept ourselves may be the first step in accepting others.
Likewise, I think people are less tolerant of people who engage in behaviors which they find repugnant in themselves. I'm reminded of the cliche of the newly sober man or woman who is intolerant of anyone drinking around them. I once asked my mother what she disliked most in other people. She spent 3 minutes telling me how much she disliked people who talked and talked and talked, repeating themselves over and over and over. And I smiled.
Working on our own program and addressing our own shortcomings may be the key to accepting the fallibility of others.