I have the reputation of being a bit of a pedant. I get annoyed by the misuse of English. Here are my top ten errors.
1 Pronouncing 'aitch' as if it began with one. 'Haitch' comes, I think, from Ireland where they have several idiosyncrasies in pronunciation - 't' for 'th' is a common one. 'Haitch' is now common among young people in the UK. Youngsters seem astonished when told it is a wrong pronunciation. Is school no longer compulsory in Britain?
2 The misuse of 'fulsome'. Praise is always fulsome. If only people knew what this really meant they would cringe with embarrassment. It is not a strong form of 'full'. In fact the word is derived from 'foul'. Fulsome praise is cloying, insincere, exaggerated, Uriah-Heap-like, praise. Sometimes when I hear the phrase I am not sure whether the user is being ironic.
3 Foetus. We English like our ligatures (not diphthongs, that's something else) in words like haematology, anaemia, oesophagus etc, but there are good etymological reasons for this. Take a word like 'aetiology' which Americans spell as 'etiology'. It sounds like it ought to be something to do with 'etiolate' but this has a quite different meaning and is 'etiolate' in British English too. But 'foetus' is a false etymology. It should be 'fetus' in British English also.
4 Apostrophes. In "Fish 'n' chip's" one of the apostrophe's is wrong. An apostrophe indicates that something has been left out. The 'n' is an abbreviated form of 'and' and therefore the apostrophes are correctly placed, but they have no place in a simple plural. In possessives, 'Archilbald's book' really stands for 'Archibald his book' though how that works for 'Mary's pencil' I'm not quite sure. The most irritating misuse is for the plural of a date. The 1970's is wrong and the 1970s is right. Please don't confuse 'its' with 'it's'.
5 Between you and I. Would you say 'between we'? Of course not! Perhaps this is a reaction against the equally incorrect "Me and my mate went to the pictures together." If so it is worse being not just ignorance but a misplaced elegant gentility.
6 Split infinitives. Silly rule! To boldly go and split them is my definite ambition.
7 'Anticipate' meaning 'expect'. This is what Fowler called 'slipshod extension'. If you anticipate something you do something about it beforehand. If you anticipate an attack by the Taliban, you forestall it, you don't just wait for it to happen. CS Lewis called this misuse of words 'verbicide'. Our vocabularies become impoverished unless we maintain distinctions.
8 Here is a battle already lost. 'Meticulous' is really a synonym of 'pernickety' rather than 'scrupulous'. It means more than taking a lot of care, it means doing so in a fussy and annoying way. Verbicide!
9 'Decimate' means to reduce by one tenth not reduce to one tenth. Not too bad if you win a war with 90% of your army intact, but to win with 90% dead would be something of a Pyrrhic victory.
10 'To claim' means to demand recognition of a right. Hence we have a claim that Humphrey Bogart, Walter Houston and Tim Holt fought over in "The Treasure of the Sierra Madre". It does not simply mean 'to assert'. Words are tools and like all tools it pays to keep their edges sharp.