When bolting down a porcelain toilet, how tight is "too tight"?
I start by hand tightening as much as I can, then I tighten a little on each side and check if the toilet moves.  If it does then I tighten a bit more, check and repeat until there's no movement.  You're trying to avoid bowl movement, so that it doesn't shift or fall over, not to hold the floor up by the toilet bolts.

As tight as you can go will probably snap the porcelain (with a good socket you can torque a nut onto a bolt quite a bit).  Until you think it's about to snap is just guessing.

Snug.  No movement.  Enjoy.

"Too tight" is a sixteenth of a turn past where the porcelain snaps :-)