I hadn't intended to imply that the graphic was offensive, nor do I think that most Japanese people would find it so either. I was just pointing out (perhaps imprecisely) that perceived appropriateness in Japan is highly context dependent, with work environments being amongst the most conservative in this regard. The degree to which people seek to avoid offending others (as compared to the US) is quite at odds with a "if someone doesn't like it, it's their problem" mentality.

Trains and parks, by contrast, are generally considered an appropriate context to consume these kinds of materials. That being said, book covers are also far more commonly used for exactly the same reasons.