My current record holder is one ebook where the author decided to use different fonts for different characters. After reading a couple of pages, I stripped the embedded font references to the generic versions since I didn't mind the alien's communications in sans serif and the human's speech in serif. If nothing else, it was giving me a headache trying to remember which font referenced which character and the mix of fonts on a page took me back to the old days when documents earned the nickname
ransom notes.