It's happened a fair amount of times, and since it won't hurt to actually have a thread like this up, it'll now be done.
Now, a few things that are easy to do when you want to discuss what happens in the latest manga/anime that you've read/watched, and really want to discuss with your biggest internet friend ever. Alas, others here have not read/watched it, and will curse at you and shake their fists at their screen in the hopes of your humiliation!
So, a few easy things to do, in case you didn't already know.
1. Use the SPOILER tags! The simplest thing, merely click on the "Insert Special Item" button and check the SPOILER tag. Your frivolous speeches about how Naruto is ACTUALLY a badger in Naruto Episode 112 will be hidden for the general public that hasn't had your grace and luck to be able to read/watch such a manga/anime before you.
An easy sample on where this button is.

2. Make sure people know there are likely to be spoilers in the thread. Put up a spoiler warning in the thread title, or during your post before you post the spoilers. (While there might be a spoiler tag on the thread title, this should not stop you from using the spoiler tags anyways.)
3. If you're replying to a spoiler thread, and having seen the subject in matter yourself, make sure you post spoiler tags yourself as well, since some people might read your reply and still easily figure out what the first spoiler was.
4. For those of you who use Quick-reply, or just can't be bothered finding the button, you can also easily just stick in the code for it as well around your selected post, shown here:
CODE
[spoiler]Your text here! :O[/spoiler]
Using these simple steps, you'll easily be able to discuss large spoilers, without bothering the rest of the people that reply in the thread.
Thank you for your cooperation.