I hate being spoiled involuntarily.

I don't mind spoilers in the appropriate context, like a discussion thread about a show/game/movie/whatever. Sure, it's nice to be able to read spoiler-free discussions and reviews of things, but I don't think that's a realistic expectation for dedicated discussion threads and the like. What does annoy me, however, is when someone does spoil stuff in a public context where people have little control over what they do and do not read - Facebook, Twitter, IRC, discussion threads about unrelated things, or what have you. That goes for vaguespoilers too, like "OMG [character name] ;____;". Not mentioning specifics doesn't mean I won't be watching that character like a hawk and be less impacted by the event in question, and probably missing other plot subtleties in the process.

It's not that I consider it an unalienable right not to be spoiled or anything. I don't even expect not to be spoiled, being an on-demand consumer who often watches/plays things long after they're aired/released. I just think of it as a matter of etiquette that takes very little forethought and effort to follow, and I usually find it a bit thoughtless or even rude to ignore it.