It is interesting to teach slang, but only if the students are very very good at what they know and can understand you fully. I think for me teaching something like this will only lead to more and more words I have to explain to my students until the whole point of teaching slang which is to induce a fun atmosphere gets lost in translation. We can all save the slang for good times in the evening when we get together with other foreign teachers. If you do choose to work in the ESL field you will get a chance to learn how fun the English language really is.