Thor goodneth thake, Granthnetterth!
What a fuss and so much hatred expressed. Like Classic I had problems with f and th, also pronouncing sh and s as 'th' when I was a child, Unfortunately my full name had 1 Sh 1 th and 3 esses in it - nightmare. It made me a very shy child, who preferred NOT to talk unless necessary. The problem was only resolved when my second teeth came in and I have scarcely stopped talking since.
It is obvious from the comments above that yous (that's You plural) can understand perfectly well what the criticised people are saying, so why all the fuss?
Personally, I love to hear different accents, dialects, etc. and can understand Youff Speak etc. I do find it amusing rather than annoying when cut glass English speaking news readers attempt to pronounce Scottish place names such as Auchtermuchty, Lochwinnoch, Ecclefechan, indeed anything with the 'och' sound therein without benefit of having learned how to make that sound. I am sure there are many examples throughout the UK where, unless you are local, you have no idea as to how to pronounce eg Milngavie, Brechin, Sauchie, Kirkaldy, and names such as Menzies.
Perhaps it is the time and effort that our generation were forced to expend on talking 'properly' that makes people so angry with those who speak in what is considered lazy or slang.