Using correct grammar is something that is quite important to me, but if I'm in a situation where it would be extremely odd, I tend to let loose a little and slang a bit with them.
Of course, using different standards for different sets of people is certainly good practice for drama classes and exams... >.>
Gaian Grammar Guild
The Gaian Grammar Guild is a refuge for the literate, a place for them to post and read posts without worrying about the nonsensical ones.