I've been judged for using "proper" grammar, which is to say that my spoken English more closely resembles written English than most people's. The people who are put off seem to object on the assumption that I am judging them harshly for not speaking the way I do.
I seek to be more descriptivist and less prescriptivist about language. Most of our rules about grammar were shoe-horned onto the language by a Latin professor which, as a friend of mine once eloquently said, is rather like "trying to put a Barbie Doll dress on a Cabbage Patch Kid".
The point of language is to communicate and things such as slang and informal usages of language, when standard for a given community, facilitate communication within that community. Formal language, up to a point, has the advantage of generally being understood by a wider audience and is thus generally considered to be "correct". But most of my deeply held "this is correct, that is wrong" beliefs about language are unravelling here in the UK as all these silly Brits seem to think that the way they've been doing it for hundreds of years (usually slightly fewer hundreds than we Americans) is, in fact, the correct way and that my usage is the non-standard one.
