I am strongly irritated by most English errors. However, I am strongly inclined to make odd slips resulting in typographical errors, especially by adding or omitting suffixes inappropriately, or repeating words, and so am guilty mysef. I always preview my posts and things still slip through, making me edit them. I have been known to edit out typos from posts that are six or seven years old when I ran across them again for whatever reason.
Because of these things, I restrain myself from most commentary regarding online post language errors, especially those that appear to result from basic mistakes.
However, when a poster's written words become unintelligible, I can't stop myself. I have to ask what they really meant and this, regrettably, often requires pointing out what it was that caused the issues.
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Beyond errors, though, is the realm of obnoxious laziness. People who can't be bothered to even try to use basic capitalization and punctuation. When I come across this, I skip over it. If the first post of a topic is like that, I just skip the whole topic.