My only actual mistakes in your list were not to close the bracket and to omit one comma. But, I'm not the one saying how terrible other people's SPaG is, and how it boils my piss and how things (that are actually, factually correct) are wrong. Because if I were that person, that would be akin to me saying "Gah, people can't do maths today, can they? I mean, my friend kept telling me 2 + 2 was 4!"
I make mistakes. I make errors. We all do. To start a thread effectively saying "the people who say/write this are thick" is on a different scale.
Any sentence I may have copied from Google (and I don't actually think I have, but can't recall) would have been quoted correctly. I don't need to look this stuff up, it's my bread and butter.
I haven't claimed to be superior to anybody. I have pointed out how vile it is to start threads criticizing other people's SPaG, and asked those doing it to think, for a second, how the "could of" writer might feel if they were to read these nasty posts. A bit of reverse psychology does seem to work, doesn't it? Look at how humphy most of the "could of makes my teeth itch, why, on a thread the other day I saw..." posters when I point out their errors. Many of which are just as bad as "could of". I don't think there are many who agree with the OP who haven't dropped just as bad a clanger as using a "could of" while they pat themselves on the back. There is nothing "cheerful" about slagging off someone's poor language skills. And you cannot, hand on heart, pretend that there is.
But anyway... (don't start, you've already been told that And can begin a sentence, and so can But. Context and situation is all, and I would not encourage my students to do it when there are other words they could use instead, but it isn't wrong)
"did use" = emphatic use of auxiliary verb.
The dash is a perfectly acceptable alternative to a colon, again, for emphasis.
Any sentence I may have copied from Google (and I don't actually think I have, but can't recall) would have been quoted correctly. I don't need to look this stuff up, it's my bread and butter.
What a very strange extrapolation you make, that I don't work. I shall tell my school, the university, and my publisher that I am but a phantom presence. Klaxon- some people on MN live in different time zones to the UK, and lecturers have free hours.
But, to keep in with the lighthearted vein you insist is prevalent on this thread...you do know what the majority of MNers say about username usernames? 
Could you point out any grammar mistake I have made? Or spelling mistake? Seriously. I'll give you a missing comma and a non-closed bracket, though that's punctuation obviously. But grammar and spelling- in my line of work, I do need to know. Particularly as all of my posts are riddled with them.