I don't claim to be the God of English, and I don't claim to never make the mistakes I hate myself! Also I realise some people find all of this more difficult or weren't taught properly in the first place.
The things that commonly annoy me, and this is in general everyday use of English: (some of which have already been pointed out):
[list][*][b]Use of abbreviations or "chat"-style slang[/b] which forces the reader to stop to think what is actually being said.
[*][b]Lack of capitalisation and general punctuation[/b], especially when it leads to difficulty in ascertaining exactly where the start and the finish of a sentence is. Conversely, excessive capitalisation is annoying. Basically it's only capitals if it's the start of a sentence, an acronym [u]or[/u] a [i]proper[/i] noun (eg. a name of a place or a person), NOT if you just feel the word should have capitals.
[*][b]Poor and inaccurate spelling.[/b]
[*]Use of "your" when it should be "you are" or "you're". To check it, try replacing it with "you are" and see if it still makes sense. If it does, then you should use "you're" and if it doesn't you should use "your".
[*][b]Incorrect usage of "their", "they're" and "there".[/b] To check it:[list=1][*]If it makes sense when replaced with "they are" then you can use "they're".[*]If referring to an object as belonging to someone else, as in "it was their apples" then you should use "their".[*]If saying "over there" then you should use "there".[/list]I think the most common mistake is when people mean to say something like "they are going to fix the tap tomorrow" and they say "their going to fix the tap tomorrow" instead.[/list:o]
[list][*][b]Apostrophes and plurals[/b]. Apostrophes are used to show either ownership or contractions.[list][*]Ownership: if the dog belongs to Jack, then it is "Jack's dog". If you need to add an apostrophe and an "s" to a name that already ends in "s", like "Charles", then you can make it "Charles's" or you can say "Charles' ". [u]The only exception is when using the word "it" to say that the "dog" belongs to "it", in which case [b]no[/b]apostrophe is used and you just say "its".[/u] The [b]only[/b] time you use "it's" with the apostrophe is when you could be saying "it is" instead.[*]Contractions: like converting "they are" to "they're" or converting "it is" to "it's".[/list]Now, if you want to make a word plural, ie. there is more than one of the object, like "dogs" or "cats", then most of us already know you just add an "s" unless it's a word like "sheep". [b]BUT[/b] you [u]never[/u] use an apostrophe and then an "s" because it's NOT a contraction and it's NOT showing ownership of anything. If you need to show ownership where the owner is a plural, like the toys that all the dogs were playing with, then the rule for showing ownership still applies: you have "dogs" (plural), and the word ends in "s", so you just add an apostrophe, optionally followed by an "s". In this case, you could say "Go and pack up the dogs' toys." If you had said "dog's toys" then you mean there is only one dog, and if you had said "toy's" instead of "toys" then you are just wrong!
[*][b]Use of ie. and eg.[/b] ie. equates to "in other words" and eg. means "for example". ie. is often used when eg. should be used instead.
[*][b]Starting a sentence with a number[/b]. Sounds stupid, but if you have to start a sentence with a number then it should be written in words, not in figures.
[*][b]American spelling[/b] like "color" instead of "colour" and "standardize" instead of "standardise".
[*][b]No paragraphs[/b] make a big wad of text hard to read. Ever noticed how newspapers paragraph all the time? That's so you can read it easily. Generally though, the people on the forums who do post lengthy posts paragraph anyway, so it's not much of an issue.
[*][b]Technically incorrect grammar[/b], although this is only because I am quite pedantic!!
(like when people say "I'll try [u]and[/u] do it" when really they mean "I'll try [u]to[/u] do it")[/list]
Most of all the apostrophes annoy me, like when "All CD's are 20% off". There is no reason to use an apostrophe so it should be "CDs". Similarly, if you were talking about G classes or VQDW wagons (to make it more relevant
) you should not say "I saw lots of G's and VQDW's today" but instead "I saw lots of Gs and VQDWs today". The only problem I have with that is that it's tempting to use an apostrophe in some situations like that, however incorrect, just to ensure people understand what you say.
Like I said at the top, I am pedantic so I take care to ensure anything I write is gramatically correct, but I know a lot of people don't care or don't know, so don't take it personally if you don't write "correctly" according to the above!