I am a grammarian. I am. I adore grammar. I cannot believe that I did not learn to diagram a sentence until I was at university, but unfortunately I grew up in an educational system that kept switching back and forth between phonics and 'whole language learning,' so grammar was barely even on the radar. I learnt the basics (nouns, verbs, adjectives, adverbs, prepositions), and sort of learnt when it was proper to use 'I' rather than 'me,' although the latter came with a 'rule of thumb' explanation rather than an actual grammatical rule to follow. Had I learnt how to diagram a sentence then, I would have clearly understood when it was appropriate to use 'I' versus 'me,' because I would have understood the difference between nominative (or subjective, in common English) and objective cases. I would have been able to describe when it is appropriate to use 'who' rather than 'whom' to my friend before the SATs more clearly than 'use whom if it has a preposition in front of it.'
There is a certain grace and elegance to a diagrammed sentence. A sentence diagram shows exactly what part of speech each word is, and how as this part of speech or that part of speech, each word interacts with all the other words in the sentence. Is the pronoun referring to someone the subject of the sentence? Is it the object of a verb or a preposition? Is the sentence written in passive voice or active voice? All of these questions are answered easily when one can see the spider-web-like diagram that shows that THIS word is the subject and THAT word is the object, and THIS word is a preposition and THAT adjective modifies THIS word or THAT phrase. It eliminates the grey areas of understanding in what can be a complicated and twisted language. But, as I said before, I did not get to see this elegant way of explaining grammar until I was grown. So I learnt 'rules of thumb' instead. The most common rule of thumb was used to determine whether to use 'I' or 'me' in a sentence. It was quite simple really: If speaking of someone in addition to oneself, drop the extra person, as if one was talking simply about oneself. If, solo, 'I' sounds better, use 'I;' If 'me' sounds better, use 'me.' That's it. No need to understand that 'I' is nominative (or subjective) case, or that 'me' is objective case. Just drop the other person, and use the pronoun that sounds right solo. (E.g. Your mother and I thought it best. 'I' is correct because it would be correct to say, 'I thought it best.' || It is a gift from your sister and me. 'Me' is correct because it is correct to say, 'It is a gift from me.') Many persons seem to struggle with this (or, more likely, simply forego the bother of figuring out which pronoun is correct), and instead use 'I' as a default. This probably stems from the fact that, as children, it was (incorrectly) badgered into their heads that 'ME IS ALWAYS WRONG,' which is not the case at all, but seems that way because of most children's proclivity to say shit like, 'Me and Johnny got into trouble today.' So persons default to using 'I' in all cases, which sounds just as stupid as misusing 'me.'
Now, as an avid grammarian, it is natural that such things irritate the piss out of me. I can find it in my heart to forgive such transgressions (grudgingly), because the fact is, most persons cannot find their way to BEGIN to diagram a sentence, much less understand such concepts as 'nominative case.' What really pisses me off are the persons who parade around with an air of smug superiority because they are oh-so-much-smarter-than-you, who get this shit wrong, and then wig-the-fuck-out when it is pointed out to them that, yes, dear, you may have a degree in English, but even you do not seem to know the difference between nominative and objective cases. I know, because I gave up that fight a long time ago with someone who no longer matters. There is nothing quite so annoying (nor quite so laughable) as someone who is convinced she is smarter than everyone else, and continues to disprove it every time she opens her damn fool of a mouth.
And do not even get me STARTED on misuse of reflexive pronouns, or the fact that APOSTROPHES HAVE NEVER EVER IN THE HISTORY OF EVER HAD THE POWER TO MAKE A WORD PLURAL.