At a certain point with things that are big in pop culture and old you can't really expect to avoid spoilers. People aren't going to tip toe around that forever.

But yeah, it is common courtesy to avoid spoilers in titles and thumbnails and use spoiler tags unless it's a thread that is obviously going to be full of spoilers.

I saw one recently where someone was like "wow, I just started the game and I'm hyped X character is in this" and then immediately people started replying with how cool the boss fight where they get turned into a demon is. (－‸ლ)