While making a hard and fast rule for every kind of 'unpleasant flavor text' is impossible, I think for cases like the post in question it's rather simpler.
Terms like rape, assault and murder are never necessary to convey the mathematical content of a question. Further, these terms are going to be off-putting for a fair portion of the audience. For a smaller (but I think still non-negligible portion), such content can be outright traumatic. It shouldn't be there, especially not in the question title.
Regarding some of the points made in the comments, I do not believe the fact that the statistics or context is real is a good enough reason to include that context in the main body of the question, or even worse, the title. I don't think there's any issue with someone giving the real world context, however grim, in a well sign-posted spoiler tag. But it should be possible to engage with the mathematics of the post (and, especially, to read question titles!) without having to think about rape/assault/murder.
This is Mathematics Stack Exchange, and if the context detracts from user's willingness to engage with the mathematical content of the question, then it should be, at least, avoidable. This is also consistent with the guideline that questions which are likely to generate discussion rather than answers (especially off-topic discussion) should be avoided.
Finally, I disagree with the rule of thumb that quid suggests about news media. If you are going to read a newspaper or watch the news, you know upfront you are possibly getting presented the worst reportable aspects of human activity. This is not so if you are going to visit a website dedicated, quite explicitly, to answering mathematics questions.