I don't know why it hasn't been done before...
Just had to make a group for the terrible instructables. If you've ever felt the urge to point out a lame instructable, here's the place to do it.
Feel free to post nominations in here.
Of course, it's hard to follow the "be nice" policy with something like this. Really, though, if the instructable was that bad, the instructor usually didn't actually care to do it well.
If they did try, and it just turned out bad, then they can still be added. Including a few tips on their page to encourage improvement wouldn't be a bad thing to do.
Mostly, though, this is for those really terrible instructables that really should be deleted. Something like "Make light from matches. Instructions: Go to a dark room and light some matches."
Have at it.