Back in the 90s I learned the hard way that you do not post a spoiler of a show in the headlines ten minutes after it ended on the East Coast this was on the usenet and I was new. So I learned about spoiler spaces and have used them since and devised my own rules.
One. A spoiler should be about eight lines long. That is why my spoilers contain the word spoiler with each letter for each line.
Two. Spoiler space for that season of a show thats airing or close to season finale after it aired.
Three. Spoiler space for previous seasons optional. My general rule is not needed. People who already are watching know what happened in previous seasons.
Four. Shows off the air. If its just off the air use judgement. A show 10 years ago no.
Five. Movies if they are still in the theater yes put a spoiler. Just arrived on tv spoiler. More then a year old. No. People who were interested in the movie have already seen it and the rest well either they are not interested or already know since the internet is essentially one big spoiler.
Six. Books. Mysteries use a spoiler always. The rest use judgement. Less then a year old put a spoiler.
Like, do not like?