Honestly, I believe it should but must be contained and broken down in a form which enables the student to grasp why, when and where they can use those sentences. As it is, nobody really speaks "formal" English anywhere anymore unless it's a business meeting which requires technical terms and proper vocabulary. But lately, people tend to think they can say anything with a slang and get away with it without realizing that to others, it could come off as a form of insult lol