Maybe everyone already knows about the Oxford comma and the crazy stripper thing. I just learned about them. Anyway, here goes.
Consider (1) "x, y and z" vs. (2) "x, y, and z". The difference is that (2) has an extra comma before "and". I always thought that (1) vs. (2) doesn't matter, so long as you pick one and stick with it, maintaining consistency. But some authorities feel strongly that (2) should always be used. Indeed the extra comma in (2) is called an "Oxford comma", because the venerable Oxford University Press has insisted on its use for as long as anyone can remember.
Oxford has a point. It turns out that use of the Oxford comma eliminates the possibility of confusion that can arise otherwise. For example, consider the sentence, "We invited two strippers, JFK and Stalin." It's not clear whether that means two strippers plus JFK and Stalin, for a total of four people, as in the left panel below, or whether the strippers are JFK and Stalin, as in the right panel.
In contrast, inclusion of an Oxford comma renders the meaning unambiguous: "We invited two strippers, JFK, and Stalin" clearly corresponds to the left panel.
The wacky example and pictures were created by a Dallas high school teacher and used in class a few months ago. Local parents were suitably outraged. Read about it here.
(The pictures are CBS Dallas screenshots. Thanks to Hannah Diebold for bringing them to my attention!)