When writing articles or even presentations, I've found that demonstrating a "bad" way saves on a huge number of questions (and, contrary to popular belief, there is such a thing as a bad question).  It also causes people to sit up and pay attention because, a lot of times, I've done enough research to know what the most common bad ways of doing things are.  It first captures the attention of people that use the bad way and it also kills their thoughts of "Well... we've always done it this way" or "Well... we've never done it that way before".

It's good for me, too!  It keeps me from exploding when someone feels compelled to interrupt with a question wanting to know why I'm not using the "Best Practice" of using something like an rCTE to count.

One of the measures of a successful presentation seems to be "interaction from the class".  I learned a long time ago that if that interaction is in the form of questions, then you might not actually be doing a good job as a teacher.  That frequently means teaching the bad along with the good because <drumroll please>, much of the "class" is already using the bad methods and, even if they don't realize it, they're there to learn a better way.  If they're a total newbie at what you're trying to teach, then they have also been educated as to what to watch for as a bad method in the future and can help spread the knowledge more quickly than any of us could ever do alone.

Heh... sometimes you do have to teach that the pan is hot and do it without burning the student.