Doesn't apply, not the same conversation. Discussions about limits on spoilers isn't the same as teasing someone for lacking knowledge on the same topic.
2 weeks after all seasons show up on netflix.
When everyone who will ever want to see it has done so. So never.
It's a spoiler if the enjoyment depends on surprise. It's not a spoiler if the item can be enjoyed for its own sake. Anything you can re-watch/read/see/listen to/etc and still fully enjoy isn't spoilable. Some genres (like mysteries) depend on spoilers. For other genres the unspoilability of a work is often correlated with quality.
It's a spoiler if surprise enhances the enjoyment. If there are works for which that is not the case at all, they cannot be spoiled. I'm not aware of any, are you?
So is Shakespeare off limits? Can I say whether Hercules managed to bring back Cerberus?