Jesus, you realize people just mistype things sometimes? It really annoys me when people feel like they have to come in and correct others this way, it's so condescending.
Personally, I'm grateful to be corrected on a casual and anonymous forum if it saves me from making the same mistake on a formal document, condescension notwithstanding. My response to grammar cops is either, "Thank you!" if it was due to my ignorance, or "Oops, damned autocorrect/typo/ brain fart," if a lack of attention was at fault.
Sometimes, we know just the word we want. And we know how to spell it. But we fat-finger it. Or our fingers trip. Or our brains just get the finger-tapping order a bit off.
None of these things requires an education in using the incorrect word. “Irregardless”? Give ‘em what for! Their/there/they’re? A nice reminder. Swapped a couple letters is a plausible explanation? A simple correct spelling followed with a * would suffice.