Back when I was taking my generals and actually had textbooks that I could sell back at the end of the semester, I would highlight random passages and write notes in the margin like “Balderdash!” “What nonsense!” and “Of course, that’s the ticket!” at random. Mwa-ha-ha.
Man, if writing in library books is what enrages you, I want your life.
I think it starts out with the desire to highlight “the important stuff”. The wheels fall off rapidly when the student is the kind of person to whom everything looks potentially “important”. Usually these are the folks who don’t retain concepts and merely need to highlight specific data points, so anything that is either thought or data gets the treatment. (If you’re highlighting more than 3 sentences per chapter you might as well just highlight the chapter title in the table of contents and be done with it).
Of a similar pattern are those folks who “take notes” and practically transcribe the lecture, going on for page after page, instead of jotting down one or two words every 5 minutes, which is more than sufficient for capturing the salient points of nearly any lecturer.
a. Scan the book in black and white.
b. Wear tinted glasses that don’t transmit the highlighted color.
OK, I got nothing.
As for the OP – have you tried reading just the highlighted parts to see if it’s a secret message?
I’ve never highlighted anything. I don’t get the point.
Maybe it’s because I can usually recall the book or magazine article, and I am a very fast scanner. I know that when I pick up a magazine article and resume reading days later, I invariably resume reading at the correct point. Often, I don’t trust that I did and scan back, but I always find that I was at the right place the first time.
That, and marking up an innocent book seems like an assault.
I once had a classmate who would highlight every damn line as he read. And then when he went through it a second time, he would use a ballpoint pen to underline everything he had highlighted. I don’t know how it helped him, but he got straight As.
It’s amazing how often that’s true.
I had one wonder casebook, where the person who had the book before me was an idiot savant of some sort. She (I would bet large amounts of cash that it was a woman) used different colors, different patterns, underlines, asterisks, all sorts of symbols. Almost every single word in the book had been visibly altered. About a week into class, I realized that everything in green was important, everything else was not. Double underlined, or boxed, or colored purple first and re-highlighted blue? not worth more than a glance, if that. But if it was green, I needed to know it.
I was taught to highlight things when I was very young, then I realized it was more distracting than illuminating, so I stopped.
You can always mark that out, you know (i.e. This is the part where he’s butt[del]fuck[/del]ing her.) 
While I generally agree with everyone in this thread about how you shouldn’t mark in a library book, that would have just made me laugh. I laughed out loud just reading your description. The juxtaposition of Middle English and modern vulgar slang is just too unexpected.
Just highlight all of the text in the book. Then none of it will be highlighted.
QFT.
I should have just added on. This is the part where he’s buttfucking her, in the conservatory with the candlestick.
The great and terrible thing about that class was that Chaucer was a dirty, dirty fellow. In one story a guy sneaks up behind a couple having sex and shoves a hot poker in the man’s asshole.
So I would have an immature chuckle reading these “footnotes” and then legitimately wonder if they might be accurate.
I wouldn’t be the least bit surprised if the Random Highlighter didn’t even know for sure why he or she was doing it. People often pick up habits or simply copy behaviors without examining why.
I used to work at a retail store years ago. We were required to get a phone number with every personal check. I’m not sure why that was supposed to work, as we never verified that the ten digits that people wrote on their check were in fact their real phone number, but it was a rule.
IF the phone number was pre-printed on the check, we were supposed to circle it. This served two purposes – primarily, it kept us mindful of always looking for the phone number even in cases where we did not have to write anything down, but it also made spotting the number at a glance easier if we ever did need it.
One girl who came to our store from another one in the franchise, however, always circled the entire address on checks, even if the phone number wasn’t printed on them. We reiterated to her that it was specifically the phone number we were circling, and why. It turns out she circled the address because “that’s the way they used to do it at the other store” although she could not articulate why. She apparently had seen co-workers circling phone numbers on checks at her old store and either never asked what exactly they were doing or why they were doing it, or else she’d been instructed but had forgotten, and now only went through the motions uncomprehendingly.
Furthermore, she could not or would not break out of this habit, and the whole time I knew her she carefully circled the address on every check, even though she herself would never look at them again and no one else needed/wanted/knew what that circle meant. Even after people asked her not to and explained she was confusing other co-workers. Even after arguments. She persisted grimly in mimicking the motions without purpose or understanding. As far as I know she is doing it still, for nobody’s benefit and at nobody’s request, not even for herself.
I can imagine her highlighting your books.
I couldn’t tell you when the term “buttfucking” first appeared, but both “butt” (short for the Middle English “buttok”, or buttock) and “fuck” were actually in use by the 15th century. Since Chaucer died in 1400 these words may or may not have been in his vocabulary, but they’d have been known to late Middle English or early Early Modern English speakers not all that long after his death.
And you just know that if “butt” and “fuck” are in the vocabulary, then “buttfuck” would be right behind them (so to speak).
I’m a highlighter (of textbooks). I don’t highlight in order to point out necessary information for later as much as I do it to keep focused on my task. Without my highlighter in hand, ready to highlight important information, my brain goes into zombie reading mode and before I know it I’ve read multiple paragraphs with absolutely no comprehension.
My favorite find in a used book? On page ONE, someone helpfully circled a sentence and wrote:
“Foreshadows main character’s death by drowning at end of story”
Thanks.
Could it the highlighting and the underlining didn’t serve to point out important things, but rather, help him pay attention?