What helped me – enormously – in this regard is the realization that I myself am guilty of “the worst offenses” that I see around me routinely.
That is, the loudmouth in the office behind me who offends me nearly daily with his constant inane bray… reminds me that I do the same more often than I care to admit.
The idiots who cut me off in traffic, seemingly without a thought or a care… are the ghosts of my driving past, when I used to do the same (more often than I do now, anyway, and at least when I do it now I try to be aware and at least acknowledge my error, even if I can’t actually make up for it). In addition, the morons who change lanes without signaling, or who block traffic unnecessarily when they could have easily moved to one side or the other to let others pass, well, I’ve done that, too, and no one kilt me for it, for which I’m grateful.
The fool who ruins good jokes by forgetting or mangling punchlines has my sympathy because of my memories of all the times that I’ve done the same thing.
My coworkers with occasional fake smiles and bonhomie… been there done that.
The pompous know-it-all blowhard who just has to have the last word… no, I certainly don’t recognize myself in that asshole… but I can envision myself in the role.
Et cetera.
This is not to say that I’m tolerant of everyone or for just about anything. I reserve particular opprobrium for criminals (or those who are too quick to condemn and want to lynch “criminals” before a jury does), and those guilty of deliberate and repeated rudeness, especially after they’ve been made explicitly aware of it. I reserve the right to be intolerant of some people and for some behaviors. But as a rule I recognize that “there but for the grace of God go I”, and try to live and let live.