A bit of sloven Engish is OK so long as those using it know what the correct form is. Innit, dunnit, isnit, ain't it, wasnit..... all slovenly usage of words?

The spoken words can be sometimes thought of as a form of spoken shorthand?

What's really bad is the use of bad English where those speaking or writing don't realise that what they're using is wrong. I see "were" and "where" used wrongly all the time and if you spend any amount of time reading different newspapers (not just the main "Fleet Street" titles) you'll find lots and lots of really irritating spelling misuses.