Manstein's revenge:
oddmanrush:
I had a librarian in grade school that always use to remind us to keep four on the floor.
Four what?
Legs of the chair. Some teachers and such use the phrase to tell kids to quit leaning back in their chairs and balancing on 2, which risks falling back and getting hurt, as well as damaging the chairs which were built by the lowest bidder.
Personally, I'm all for "warn 'em once, then let 'em learn the hard way"