1. Would of/could of/ should of - no I'm not naming a Beverley Knight song. This is where people hear the compound word 'would've', assume it's a shortening of the words 'would' and 'of' rather than 'would' and 'have' and pronounce as such very clearly. Think about what the words actually mean!! An old manager of mine made this mistake once - I lost all respect for her instantly.
2. Like - this should be used in phrases such as, 'I like cake' or 'she looks like Jennifer Aniston' (for instance, I've never met anyone who looks like Jennifer Aniston, although I do like cake). It is not to be used in phrase such as, 'I was like so annoyed' or 'it's like what's going on?' I am guilty of this weird lingual phenomenon too and I am seriously considering starting a 'like' jar instead of a swear jar to purge myself of the hideous verbal disease.
3. Text language - if you're texting and running out of characters, fine, shorten away. But don't send me e-mails with words like gr8, lol or l8r, there's no character limit and therefore no justification. And if you actually write these words with pen and paper, well, you deserve some form of punishment.
4. Shock tactic language - people who swear or use language relating to potentially offensive matters just for the sake of it. It's neither big, clever nor funny, it's just a lazy use of the the gift of speech to get a bit of attention. If you want attention, learn to speak about interesting things.
5. The wandering apostrophe - a while back I went past a shop with a sign saying Baby Need's. I wanted to weep.
6. Their/they're/there - Their is a plural, third person possessive noun (if my grammar lessons serve me correctly), i.e. 'Jack and Jill went to their mother's house for tea.' They're is a shortening of 'they are', i.e. 'They're going to the zoo.' There is trickier, but generally it's an expression relating to place or an introduction to a clause or sentence, i.e. 'The bag's over there' or 'There are cookies in the oven.' Please, oh please, never muddle them up again.
7. Your/you're - in the words of Ross Geller, "Just so you know, Y O U apostrophe R E means you are. Y O U R MEANS YOUR!"
8. So - similar to like, this little word seems to pop up in the most inappropriate places. In fact, it is often combined with like in phrases such as, 'I was like so not happy about it' just to emphasise the hideousness of the incorrect usage of language. It is also often used at the start of a sentence, for instance, 'So I went to the shop yesterday ...' but that's not referring back to a previous statement about needing to buy something, oh no, that's the first sentence in the text! Horrible!
9. Innit - really, must I expand?
10. Effect/affect - another two words that are apparently interchangeable these days. Hence phrases like, 'I must stop playing so many computer games, it's effecting my eyes.' Really? It's producing or bringing into existence your eyes? That's some computer game.
Maybe I should be an English teacher ... no, I think I'd make the children cry.