On a local music board (which also used vBulletin IIRC), we used to have "spoiler" tags.
It would basically produce a box, similar to a quote, but be titled Spoiler, the text was the same colour as the box background, so it could only be read if highlighted.
Just for any movie talk or whatnot in OT really
(nevermind, delete this, I didn't realise til now that the forum had this capability!) Spoiler Below. Highlight to read.