All mouth and trousers
One minor but deeply aggravating example is if I use the delightful expression 'all mouth and trousers' (as I did in this feature for Real Deals on the Northern private equity market a few years ago) only to have some gormless sub in London try and change it to 'all mouth and no trousers'.
The 'no trousers' version, I have found, is a much more recent bastardisation of the original, which has become predominant in London and the South of England. It loses the precise eloquence of the original. I assume it's by confusion with phrases such as 'all talk and no action' (or, another favourite, 'fur coat and no knickers'), but such confusion only seems to demonstrate the failings that the original phrase mocks. 'Talk' and 'mouth' may be metonyms, but 'action' and 'trousers' certainly ain't - and if you think they are, that might say something about you.
Nevertheless, the bastardised form continues to crop up in the London-based mass media, causing me no small degree of irritation and chuntering at each occasion. In a perhaps quixotic attempt to reverse this trend, I've launched a new campaigning blog to promote and preserve the original.
It might seem a rather minor concern to some, but it is an issue that has inspired deeply-felt and loudly-expressed exchanges of opinion in the past. I hope that all who read this blog, and my work elsewhere, will support this cause by using the expression in its traditional and more eloquent form as often as possible.