libpng

If there were a competition for world's worst man page, libpng's would be right up there. Instead of individual man pages for each function and struct, it rolls everything into the one huge document. That would be acceptable if it gave descriptions for each of the functions, but it doesn't, instead providing an nigh-impenetrable wall of text which is borderline useless as a guide or a reference.

Misgivings aside, I've managed to extract the useful information for the simple loading of a PNG image and put it in the code sample below: