During recent months we had several times when forumites, even unintentionally from their part, gave spoilers about the content of games, movies and books in places without any warnings. And I don't talk about only the IE games. These spoilers severely ruined the experience for those people who still hadn't discovered the appropriate things themselves.
It's hard to describe one's feeling when he or she is looking forward to a game, a movie, a book, and then suddenly reads the key detail on the forum because no warnings came.
When you post something on the forum, check to things:
1) whether the thread title, or even the sub-forum title has a "Spoilers!" warning in it
2) whether the thing you're going to post about is a key spoiler about anything
For example, https://forums.beamdog.com/discussion/25272/baldurs-gate-meme-thread-ii-enhanced-edition-careful-everyone-spoilers#latest
has a "Spoilers!" warning in the title, but this warning comes only for things related to BG, - so if you want to post a spoiler about anything not BG-related, put a spoiler tag into your post.
Another example. https://forums.beamdog.com/categories/general
has a "Spoilers!" warning in the name of the subforum. So if you're a new player, don't read the discussions there, or create a discussion of your own there, with a note of not getting a spoiler, or read things there very cautiously.
Posting in any discussion in the off-topic section of the forum about other games/movies/TV-shows should fall under the same rules. Don't forget that not everyone, even if they're interested in the same game/movie or book, knows as much as you.
Don't forget that one of the Forum rules is "Don't spoil the fun".
There are measures everyone can take to avoid spoiling things for those who haven't experienced the game (and the same can be said about other things) yet. If you're going to ruin the plot, announce it beforehand.
One of the great things about any release is that it's exposing a lot of new people to what the release has to offer. That great thing is ruined, and not in a small way, when elements of the plot and character stories are announced or bandied about with no care for who's listening. So the short version is, if you're going to discuss the plot or anything else that might "spoil the fun" for somebody, wrap the content in spoiler tags. Spoiler tags look like this (without a space between [ and spoiler):
[ spoiler]This is a spoiler[/ spoiler]
[ spoiler=you can announce things that are put into a spoiler] This is a spoiler[/ spoiler]
This is how it looks like.
This is a spoiler