By the way, I'd just like to mention that actually it was a course book that really opened my eyes to how much out there is taboo. It's a favorite: Innovations Advanced, and kudos to the authors, Hugh Dellar and Andrew Walkley, for going out on a limb. The book isn't offensive, often broaching delicate subjects obliquely; and sometimes more directly. For example, in chapter four, The Law, an Arab-English woman tells her friend about her holiday and about the problems she had going through airport security. She implies she was picked on because of her race and creed, and suggests the anti-terror laws go too far.
It's a lexically rich listening, and the follow up discussion is always interesting: students discuss any problems they've heard of going through airport security, and if they agree that the new anti-terror laws go too far. I've never had any problems with this activity. In fact students generally have lively, enjoyable conversations, and I find it interesting as well because I'm curious what they have to say about it.
I'd like to mention that as a one-off activity I recently showed my students the film, Notting Hill, which I actually thought was fairly innocuous. By the way, I normally recommend students watch English films and TV series with no subtitles in order to focus on listening comprehension, to develop their ear. However, in this case I opted to focus on vocabulary so I showed it with English subtitles so they could easily jot down unknown lexis. In any case, many of their queries had to do with swear words, for example, 'bollocks', 'bugger', 'a git'.
So another big taboo area for course books is swear words. Students normally aren't exposed to them in class, so when they do come up, for example in a film, it's understandable that they want to know what they mean. Actually to help them out, and for educational purposes only, I occasionally swear a bit in class myself. After all, it's authentic English. For example, if I make a mistake, I'll freely confess to my students that, 'I messed up', or even, 'I fucked up'.
If students seem curious about swear works and want more, a favorite technique to introduce new language (of any sort) is the teacher's anecdote, in which I tell them a story about something that happened to me or someone I know (I personally prefer not to read it). For example, very recently I saw a guy 'wipe out' on his mountain bike. I was with two friends, a Spaniard and an American, waiting to do some jumps. So this guy asks if we'd mind if he went before us, so of course we graciously agree, I mean, 'I don't give a fuck'.
So off he goes. We notice he hasn't lowered his seat post, a telltale sign of a novice, who probably shouldn't be doing double jumps (the dangerous kind), but 'it's none of my fucking business'. So he gets over the first two all right, but on the third one he doesn't quite make it and 'wipes out big time', the kind it's painful to watch. The three of us groan and the American says, 'Oh shit!', I say 'Oh my god!', I think the Spanish guy said, '¡Hostia!'.
Actually this is a typical thing: you get novice riders who want to be advanced without 'going through all the trouble of slowly building up their skills. I mean, I have to admit 'the guy has balls', but going over the handlebars like that 'really sucks'. Luckily he lands in sand, and when we get over there he's on his feet, a good sign, but his shoulder hurts and 'he looks like shit', so his friends take him off to a hospital: a broken collar bone is typical, but hopefully it's just a sprain. The front tire of his bike will never roll again: no way to fix it, have to buy a new one. So 'the guy fucked up big time'. Life's hard lessons, right? Well, maybe now 'he'll get his shit together' and be more careful.
So you highlight the target language on the whiteboard, and hope the director of studies doesn't pop in at that moment. Then students can discuss any accidents they've heard of, and maybe use some of the target language. Or you could prepare discussion questions like, 'When was the last time you fucked up big time?' You might want to approach this humorously, like I'm doing, lest somebody feel offended. Be sure to point out that this language is possibly offensive and should only be used with care. Yet it is authentic English, as anyone who's seen Notting Hill can attest.