In response to yesterday’s Harry Potter post, commenter Karl said, “‘Spoilers’? How can there be spoilers if you have already read the books?” My response was that books are different from movies, and I don’t really want to know what changes the filmmakers have made until I’m watching the film. I wasn’t always anti-spoiler, though. Before any of Peter Jackson’s “Lord of the Rings” movies made it to the big screen, I collected every spoiler I could click.

But sometime after “The Fellowship of the Ring” premiered, I decided that carrying around all those jigsaw-puzzly bits of movie knowledge was distracting me when it came time to actually watch a film. I wound up being decidedly anti-spoiler. And it’s not just plot details that I’d rather not hear. Case in point: If someone had told me that [warning: "Chuck" spoiler incoming] in the second season of “Chuck,” Chuck’s dad turned out to be Scott Bakula and one of the first things out of his mouth was “Oh, boy,” it would have damaged my calm. [Spoiler finished.]

But Karl’s comment has led me to think about a bigger question. Exactly what is the fan etiquette regarding spoilers? Message boards and fan sites usually have their own spoiler policies, but apart from that, most people seem to follow a set of largely unwritten spoiler rules. From my experience, they are:

1. Anything that has a plot can have a spoiler, from TV shows to quest lines in MMORPGs.
2. Either warn people before you get into spoilers, or keep them to yourself.
3. There’s a statute of limitations on rule No. 2. How quickly it expires is inversely proportional to how popular and immediately accessible it was. But if someone you care about just started watching something everyone else has already seen, it resets.

Most of the geeks I know follow the basic rules regardless of how they themselves feel about spoilers. My friend Jack, for instance, is all spoilers all the time — but he always asks whether I want to hear the latest “Doctor Who” rumor before he dishes the dirt. And for some reason, even though I know he loves spoilers, I keep asking him first — just to be polite. But then there are the folks who ignore rule No. 2 entirely, either following the theory that spoilers want to be free or deliberately trying to ruin a story for other people. The general consensus is that the latter fall somewhere in the realm between mean and rude.

And then there are those who turn spoilers into something funny. Spoilers for every movie that’s won a Best Picture Oscar, plus 2008’s nominees, anyone?

(The guys from TheFineBrothers.com also spoiled 100 movies in one take — but more people have already seen that one.)

What do you think — should spoilers be free? And am I missing any of the unwritten rules?

Here are some HowStuffWorks.com articles that bear now-expired spoiler warnings. Gee, I wonder who wrote those?

How Harry Potter’s Wand Works
How the DHARMA Initiative Works
How “The Da Vinci Code” Doesn’t Work