I think less of people who use slang with strangers. How do you feel about slang?
Why do you think less of people who use slang with strangers?
It is the language of dumb people. They can't form complete sentences.
It is rude to judge other people if you don't know them. Not everyone shares the same culture as you or language.
Not to me, I don't judge!
Slang isn't a bad thing and these people probably are just as smart as anyone else. Just because they don't always use formal language doesn't make them any lesser than you are.