R-rated movies is another great example of "is it a rule?"
There is counsel to avoid what is bad constantly, and R-rated movies get lumped in with that counsel. But is it really a rule that could cause you to be punished if caught breaking?
A lot, if not most, congregations use the Bethel rules as a guideline. In Bethel, R-rated movies were forbidden.
Every congregation I was a part of, if a pioneer or servant were caught watching R-rated movies, they faced the possibility of being removed. For the R&F publishers, it was a "talking to".
A buddy of mine, not a servant but trying to be appointed, got busted when someone saw some R-rated tapes (this was a while ago) in his house. Leaving aside that the snitch should have confronted him personally about it instead of running to elders, once it was reported, the elders requested his presence in a little meeting at the hall. Two hours of counsel on avoiding the badness of the world and stressing on him that this was not the way to get appointed.
Tell him it's not a rule and I think he'll disagree with you.