jtaylor wrote:

The little plastic operating lever on the toilet tank has a left-hand
thread. I cannot think of any good reason for this.

Normally a design incorporates LH threads where normal use would loosen
RH threads. For example if a lever were mounted on the top left of a
toilet tank such that the lever were to the left of the mounting screw,
operating the lever normally would tend to unscrew it. Since most toilets
I'm familiar with have flush handles like this, perhaps that is the reason.

GWE