That's a really good lesson to remember, and thanks for reminding me, Jollybear, although I know I'm going to forget again.
A cpl times life tried to teach me this one:
--- I once screamed at, threatened, and then shoved a deaf guy for not getting out of my way (didn't know he was deaf, thought he was just messing with me).
--- one time I was sitting on my motorcycle outside of a gas station, when I noticed this big guy grinning at me and for some reason took it as derision, so I flipped him off (was really surprised by the hurt look on his face). When I went inside to pay, I heard the big guy talk and realized he was mentally disabled, and that for all practical purposes I had just flipped off a 6 year old.
What this taught me:
--- better to let a jerk get away with being a jerk than to inadvertently offend someone who doesn't deserve it.
--- if someone is being a jerk, well, I guess you can consider being a jerk a disabliltiy so maybe those people deserve some slack too.
--- like you said: more times than not I'm misunderstanding the person or situation, so letting anger be the default reaction is pointless.
Never attribute to malice that which is adequately explained by stupidity.
----Hanlon's razor
Like I said: life has tried to teach me this countless times and hopefully someday it will stick.