Spoiler alert your face, son. Those who spoil must pay the price.
Of course there's a statute of limitations on how long we have to be careful about spoilers. We can't be expected to never discuss our favorite shows just because some people haven't watched yet. Here are the common courtesy rules for when it's safe to discuss.
TV shows - You can openly talk about a show when everyone in the world who hasn't yet seen every episode signs a waiver saying they never intend to watch it. If anyone refuses to sign or you're unable to collect the large volume of signatures, then you'll just have to keep your mouth shut.
Movies - You can openly talk about a movie when everyone who hasn't seen it yet has died.
Books - before you discuss any book, make sure everyone within a one mile radius has read every book that you have read.
The answer is never.
The First Amendment to the United States Constitution clearly states nothing addressing this. But the answer is also never.
