James while John had had had had had had had had had had had a better effect on the teacher

Lexical Ambiguity
Of course the title doesn't make sense. But if you are new to it, you'll be surprised to know that with proper punctuation, it does. Here is how an article on Wikipedia describes it.

"James while John had had had had had had had had had had had a better effect on the teacher" is an English sentence demonstrating lexical ambiguity. The sentence is often given as a word puzzle for which one must find the proper punctuation to give it meaning.Reichenbach used it in 1947 as an exercise to the reader (but as "John where Jack…"), to illustrate the different levels of language, namely object language and metalanguage.
The phrase can be understood more clearly by adding punctuation and quotation marks:
James, while John had had "had," had had "had had";
"had had" had had a better effect on the teacher.
The meaning could thus be rendered, after some reordering and changing a few words, "While John had used 'had,' James had used 'had had.' The teacher had preferred 'had had.'"

Another example:
A similar, punctuated repetition of had had appears in Jasper Fforde's The Well f Lost Plots:
Good. Item seven. The had had and that that problem. [...] 'Okay,' said the Bellman, whose head was in danger of falling apart like a chocolate orange, 'let me get this straight: David Copperfield, unlike Pilgrim's Progress, which had had had, had had had had. Had had had had TGC's approval?'

There was a very long pause.'Right,' said the Bellman with a sigh.