Ha! I would've been amused too. Though that's a different issue - the distracting from the vid one, because if my warning amused just by its very existence, it would actually set the wrong mood for the vid, which I don't think you could squeeze funny out of with a garlic press.

So it seems like for many it might be unneeded (and possibly make people think I'm paranoid, which I am) but at least a few might be grateful for it. Maybe I'll go for something as straightforward as possible - "Warning - contains spoilers for [movie]" and try to keep it as short as possible for people who don't care about the warning.