If it is in a non related Mangas thread though and not the general thread it's kinda assholish to spoil something.
Here's the rules set:
This thread and main manga thread: Everything's free game (unless it's a spoiler leak the night before)
Anime thread: Anything past the latest episode must be black barred.
Toonami thread: Anything past that point. The latest episode just had Luffy go Gear Third (or Third Gear) on Lucci. That is a lot to avoid spoiling. Though some stuff is just common knowledge thanks to time, like Franky joining the crew (also, that realization it's been almost nine years since Franky joined).
Other threads: Try to be considerate. Stuff like the Straw Hats and the time skip tend to be fair game as they're everywhere but don't scream that Sabo is alive or certain events in Dressrossa.
Source: MAH ASS!