I don't think that there.is any evidence that "the more obvious things" are actually common triggers (on the PTSD sense); there common sources of offense to that works on a more conscious level, but AFAIK that's almost completely unrelated to the mechanisms involved in triggering, even when the subjects involved relate to the source of trauma; it seems more hijacking the very real idea of triggering related to traumatic experience as a means of asserting a privilege against offense.

Now, personalized trigger warnings in a context where particular individuals are known to be sensitive to particular things as triggers make a lot of sense, but AFAICT generalized trigger warnings have no valid basis in anything that has to do with actual triggering, and those pushing them trivialize real trauma-related conditions.