How to be a mean teacher in a nice way

I sometimes find myself with feet in two different camps. I happen to know that humans, if asked to set their own limits, will set them low. I happen to know that one of themost important lessons learned is that even when you think you can't possibly do something, sometimes you can if you keep going because you have to.
I also happen to know that lots of people learn to become expert failures because they've been in situations where they "had to" do something, and they couldn't.

I enjoy when teachers find ways to set up the "mean and ruthless" scenario ... but set it up for success. Friday the 099 class was duly informed that there would be an all-or-nothing quiz on Monday, and they'd be required to exactly state the equation for the quadratic formula, and if they got one inkblot wrong, it would be a zero. And no, the teacher doesn't care that you think he's a jerk.
And, by the way, here are the exact things that students have yelled about in the past. And he writes up the really easy really little mistakes. And the student in the front row says, "I could see myself doing that." And I think to myself, "me, too, but not NOW."
THen he wasn't there on Monday, so I have no idea how well these guys are going to do. Perhaps they'll cruise YouTube for the songs... brb...