I went to college in the 1980s, and profs told us when a book or film might be disturbing-- on day one, but not in the sense of a trigger warning. It was more like, “drop the class now if you can’t handle it. Don’t come asking for an incomplete halfway through.” In film studies, it involved giving the rating of a film, and whether it was mainly for sex, or for violence. Whether anyone ever went to talk to a prof privately was between the prof and the student. I suppose it was always possible to ask not read something different, but then you couldn’t participate in class discussions. Profs might consider it for a single book out of seven, I suppose, but not for an entire curriculum. I don’t know, because I never had to talk to a prof.
In creative writing class, we had to warn people ahead of time if our stories used “swear” words, and a classmate could choose not to read a story that had “fuck” in it, but I don’t remember that profs ever told us to warn about explicit sex or violence. Maybe because few people wrote about that, because you don’t want to hear that your sex scene was amateurish.
When I was in high school, in drama class, and we did a scene from a play that had a “swear” word, we could choose to change the word, or do the scene as written, and give our class a verbal warning before we performed, so that anyone who might be offended could choose to leave. In four years of drama class, I don’t remember anyone ever leaving. The one exception was “goddamn.” We had to say just “damn” (or something like “goldarn,” if “damn” didn’t scan well), and that came from the administration, not the teacher.
The only thing I ever heard phrased as a “trigger” warning was when I was going to a film for a class I wasn’t actually taking (you could buy cheap passes to see the films even when you weren’t enrolled in the class, and I did it a lot), the prof warned epileptics that there was a strobe light scene so many minutes in, and if they needed to leave, they should feel free to do so. No one left. There was another time when the prof warned people of a very loud scene, but it was just a warning, not a “Get up and go if you need to.”
I’m totally in favor of syllabi for film classes giving MPAA rating of a film, but calling it a “trigger warning” is a little silly. In lit classes, people majoring in lit are generally aware of what happens in books in the canon, even if they haven’t read them (profs can assign 8 books a semester to English majors, because people majoring in English have usually read half of them already), and the kinds of classes directed at non-majors usually have very well-known books, that it’s hard to be surprised by the content. Even if you have managed to get to college without reading The Scarlet Letter, you must know it’s sexist by modern standards-- the book is supposed to offend you-- it was supposed to offend Victorians, for cripes sake. And, most people know, even if they haven’t read it, but spoiler just in case, that Tess of the D’Urbervilleshas a rape scene.* If you can’t handle it, don’t take the class.
*If you ask me, it’s a scene that ought to provoke class discussion that could be beneficial to a rape victim, since it’s the kind of scene that that senator would probably not call “real rape,” since it doesn’t involve a stranger in the bushes, and a pregnancy results, but I doubt anyone in the class is going to disagree it is rape, and that rapist is pond scum. Also, the scene is mostly implied. It might as well say, “And then, Alec proceeded to be the biggest shmuck in the book-- no, maybe second biggest.”
