A dozen years or so ago, my wife and I were touring Israel when our Palestinian bus driver described our Israeli guide as “zero to the left.” His diction was clear but his meaning was not. To this day we can only guess at what he meant. Today’s insult from Shakespeare may seem strange to American ears, but it refers to the last letter of the English alphabet.
Thou whoreson zed! thou unnecessary letter! (King Lear 2.2.61).
It is an alphabetical insult. Very sophisticated. Though I know a few zany, zesty zebras who might argue against the unnecessariness of “zed.”