trigger warning
n. Advance warning that a book, movie, or other material has content that could trigger emotional distress or a traumatic reaction.
Also Seen As
The latest attack on academic freedom comes not from government authorities or corporate pressure but from students. At UC Santa Barbara, the student Senate recently passed a resolution that calls for mandatory "trigger warnings" — cautions from professors, to be added to their course syllabi, specifying which days' lectures will include readings or films or discussions that might trigger feelings of emotional or physical distress.
—“Warning: College students, this editorial may upset you,” Los Angeles Times, March 31, 2014
All GSIs and professors of social science and humanities courses should undergo training comparable to that of intergroup dialogue facilitators to ensure heightened sensitivity to diverse perspectives. Instructors should also make a concerted effort to give students "trigger warnings" that alert them to upcoming class materials that could be potentially offensive, explicit or controversial.
—“From the Daily: Let's talk about race,” The Michigan Daily, March 20, 2014
1993 (earliest)
I saw "Stephen King's Sleepwalkers" this weekend and it contains a possible trigger….

This is a pretty decent horror movie, with one exception: the 2 monsters (sleepwalkers) in the movie are a mother and son who have an incestuous sexual relationship. I think that most non-survivors would find the "romantic" scenes between the two to be pretty distasteful, but for survivors I think that the scenes could be a very strong trigger.
—Mary, “Possible movie trigger warning,” alt.sexual.abuse.recovery, September 19, 1993