I don't know if it was ever a rule, but like so many things individual witnesses would make it an issue.
Much of this "You Must Not..." attitude was, I think, fostered by the constant stream of printed literature we once had. Remember there were 2 issues each of The Watchtower and Awake! every month for decades. They had to keep coming up with topics to write about. Awake! was supposed to be tracking current subjects, social trends etc. and there came to be an unspoken attitude of 'If it was discussed in Awake it's not for Christians"..So people were down on an endless number of things....soap operas, aerobics martial arts, gym membership and so on. They would also do articles on the origins of customs, pointing out the 'pagan' background, so no wind chimes, "bless you" after sneezing, games of chance....and on and on.
Even if it wasn't in print people would undertake to criticize and "instruct" others unasked on choices of entertainment. You shouldn't watch Pokemon, Dawson's Creek, Harry Potter....
While studying, right after I was announced as an "approved associate" The Brother who conducted my study invited me to go bowling with a group of brothers and sisters. .I had not been in years and had never been very good at it, but on my first turn I got a strike. I said "It must be luck, because it's certainly not skill!". The brother pulled me aside and told me severely " We don't say Luck!" and referred to scripture about "setting a table for the god of good luck.." I was embarrassed and asked "What should I say?". He said I could say I was 'fortunate'.
This, like many "explanations" sounded convincing on a first hearing, but later I thought What's the big deal. I was kidding and all I meant was it was a happy random occurence. Besides, isn't the word Fortune itself derived from the name of a false god?