I thought of this when I read Kristin's post on Student Howlers, and on commenting on it realised we are both what could be kindly termed Grammar and Punctuation "Anoraks" - my kids and hubby call me pedantic and they are probably right, but I defend my right to be boringly pedantic in the interest of good English!
One of the funniest books I read in the past decade has to be Lynn Truss's "Eats, Shoots and Leaves: The Zero Tolerance Approach to Punctuation" which is all about the mangling of the English Language by poor punctuation and grammar. The title comes from the following joke.
The bugbear for all members of the Punctuation Police has to be the so-called "Greengrocer's Apostrophe" which renders every plural noun a possessive. "Apple's - 6for €1" is a good bargain but gets me off on a rant every time I see it.

The wonderfully curmudgeonly John Humphrys of BBC 4 "Today" fame has written another hilarious book on the same language assassination, called "Lost for Words: The Mangling and Manipulation of the English Language" . Both these books are just the tip of the iceberg of a whole genre of books that lament the sloppiness and lazyness that has resulted in kids being taught English by teachers who never learnt the basic rules of good grammar. Children who don't know how to "speak proper" are writing essays in txtspk ( has been done, in the UK an exam essay was submitted that had been written in the text shorthand that is the first language of all digit-happy children from their pre-teens).
So I was gobsmacked with the poster for the night classes, and wondered how long it would be before someone realised the bloomer. That would be about a week! The school is a very reputable secondary and post-leaving certificate college that runs excellent Fetac courses. I mentioned it to a colleague who had also noticed it. He said the principal had become aware of it, and was probably highly embarrassed that it had been printed and

I hope I am not being holier-than-thou in all this - it is just something that bugs me, and I am not a grammar whiz by a long shot. I was appalling in school in formal grammar; parsing and analysing sentences passed me by without as much as a glance, and I am totally at odds with the rules of adjectives and pronouns and verbs. One thing I did learn in school and at home was to spell correctly and use "proper" grammar almost intuitively - from a lot of rote-learning and by reading widely. My mother was very intolerant of lazy speech and I would never get away with quaint colloquialisms like "I done that" so I guess a lot of it is pretty ingrained.
Thanks to Kristin for inspiring this post, and apologies if I've annoyed some of you by being a tad pedantic on my crusading hobbyhorse!