My mom was complaining the other day about how her boss, who is an Elementary School Principal, doesn't have very good spelling or grammar, which is just incomprehensible to me. Not that schools are doing much to improve the spelling of the nation, what with their use of "Best Guess Spelling".
My rule is that an intelligent person is always curious, which leads to being well-read.
Anyone who has the intelligence to be well-read will unavoidably acquire some skill in spelling,
punctuation, grammar, vocabulary, and sentence structure by osmosis. That skill can be greatly
enhanced by primary and secondary education, but there's no substitute for years of reading.
Ergo, anyone who demonstrates atrocious spelling, punctuation, grammar, vocabulary, and
sentence structure is not very intelligent.
I've personally never known anyone who is an exception to that rule, though I'm sure they exist.
You probably have to go outside civilized society.