Um, I, ah, used to teach English a couple decades ago. We, um, focused on pronuciation and stuff. Until the last day of class when I taught a lot of slang. Needless to say, one day of hearing my extremely quick students bark out “bullshit” ad nauseum to me was enough. I swore to never, ever go against my instincts and teach slang at the beginning of the semester.
Yeah, I work on pronunciation and such… but I want my students to be able to talk to English speakers… that means understanding where English speakers are coming from. THAT means telling them that a LOT of the jokes, etc. that they hear in English have to do with sex (even if they don’t understand the idiom, slang, etc. that they are hearing…)