It is a "spinach in the teeth" or "toilet paper on the bottom of a shoe" or "skirt hem stuck in pantyhose waistband" situation, IMO.

Going by the Golden Rule, *I* would want someone to tell me if I were misspelling something. And I'd prefer to hear it from my close friends.

But out in the real world, people often become arch, snotty, and defensive about these corrections, e.g. "I suppose *you're* perfect!", or "I wasn't an English Major in college!" (Uh ... neither was I. Computer Science, thanks, and what we're talking about, I actually learned in the 4th grade. You know. Back when I was eight years old?)

Imagine someone reacting this way if you told her her skirt was tucked into her pantyhose:

<flounce, flounce, skirt still stuck in pantyhose waistband and ass hanging out for all to see> "OH! I suppose *YOU'RE* perfect, huh, Mrs. Grundy???"

Yeah.
Whatever.
That's my ONLY motivation for telling you, to establish my superiority.
Sure.
Your funeral.

It's such a sticky sitch, because misspelling a word is not as blatantly embarrassing as having your tushie out. Then again, I work as an editor, so it's pretty much my job / expected that I'd be niggly wiggly about things like that. If I overstep my bounds, I can just blame it on my being some sort of workaholic / lack of boundaries person.