I'll be the first to admit it. I am a grammar snob - and I am getting worse.
A sentence that ends in a preposition (Children are fun to spend time with.); a mismatched subject and pronoun (A teacher should always watch their language.); non-standard word use (Irregardless, the show must continue.) and little things like using a qualifier with an absolute (The song was somewhat unique.) are all fingernails on the chalkboard* to me.
I am forgiving of spelling errors but not of homophonic errors (They're trip to the ocean was uneventful.) There are plenty of word usages that still confound me (lie and lay, ensure and insure, adapt and adopt). I'm positive that I make errors that must drive other grammarphiles nuts. And even I will admit that many rules of language use are arbitrary, useless, and dated, adding little if nothing to the clarity of expression.
Grammar bigotry is probably a symptom of some deeper, more psychotic condition that compels a person to divide the world into acceptable and unacceptable levels of competence and therefore acceptable and unacceptable sorts of human beings.
I promise to do better to recognize my own biases in this area.
If you promise to use fewer language errors.
*Another cliche that's rapidly becoming meaningless.