The only trigger warning i’ve ever given in the college classroom was for a video that showed a good bit of spraying blood, because there really does seem to be at least some degree of aversion to gore built into all non-psychopathic individuals, for presumably sensible reasons—and even then it wasn’t so much a “trigger” warning as it was a “hey—this video shows blood, so if you’ve got a weak stomach you might want to be careful of that”.
Seriously, in my admittedly non-randomly-sampled acquaintance set in academia, trigger warnings are very, very rare. However, we tend to notice the unusual in some cases, and I’ve started thinking the handwringing over widespread trigger warnings stems from exactly that situation.