In my stories, I'm not going to pretend I'm grammatically correct 24/7. I mess up, purely because life is colloquial, and we're not striving for this perfection all the time. I also don't know all the rules, but if I do know the rules, I'll try following them if that's what my character's voice allows.
However, what I cannot get past is spelling.
Most of what we write is computer-based, and we all know the rule - red line? Mistake. That red squiggle haunts us sometimes - it haunts me, too, but because I'm strangely pedantic about spelling, it's generally when I've chosen names that spell-check despises - and it's a fantastically useful tool.
So why don't people use it?!
It's not a difficult task to right click, select the right spelling, and continue. I have come across countless essays, stories, assessments that people have asked me to proofread and edit, that are positively littered with mistake after mistake. Some of them, it's understandable if they've not been picked up - for instance, write and right, spell-check won't pick up. That is where you should give your draft to someone who can spell to proof it for you.
If you're going to use big words, please, please, understand what they mean. If you want to be a talking thesaurus, keep your dictionary handy. Not all the words in the thesaurus have exactly the same meaning as the word you originally used. (It would also be handy if you spelt it correctly. Gets the point across easier.) Honestly? Talking like a thesaurus doesn't make you smarter if you don't know what you're saying. I talk and write in this strange mixture of colloquialisms and formalities, purely because I've grown up reading with a thesaurus on one side, dictionary on the other. I've grown up writing the same way. If you don't understand the words, it's not going to make anyone think less of you if you stick to what you know.
Essays are designed to be formal. It is the point of a report to be formal. Colloquialisms and contractions have no place in a formal essay. If I am going to edit any piece, I will pare back those colloquialisms and fix those contractions until there is at least a semblance of formality to the piece. Take it or leave it, but in my experience, that's one huge criteria - that you have language appropriate to the piece you're writing.
I'm sorry for this post. I've just spent the night critiquing. This week's stories were quite good, actually, I really enjoyed most of them. This just brought up bad memories from previous crits/edits/conversations.
Lovely night, though.
And a night with music and They're Taking The Hobbits To Isengard.