Not so much grammar but pronunciation:
So many people now substitute the sibilant sound 's' for the 'sh' sound. This seems only to apply in words with the letters 'str' . So, for example, instead of saying ''street' or 'industry'...it is pronounced 'shtreet' and 'indushtry'.
This one is more an observation, rather than an irritation, but I've noticed that younger people, particularly, now don't 'segue' the 'ee' sound of 'the', when following it with a word beginning with another vowel. So instead of saying 'thee avenue", people will say ' the'( pause) 'avenue'. This doesn't offend me, though.
I hate 'excited for', rather than 'excited about'.
'Laying' instead of 'lying' ' I lay down', I am lying down', not 'I'm laying down'.
Incorrect use of 'I' and 'me'. ( Kirsty Allsop! On Location, Location, Location...much as I love the programme...
Using 'Myself' incorrectly...'Youself', too.
Overuse of exclamation marks, ( this, I truly
loathe). This was being discussed on Women's Hour, R4, this morning, in fact.
Overuse of emoticons.
I realise I'm being unreasonable, but this is Pedant's Corner...