A week after the episode was on TV for the first time? A month? A year? And with movies?

I guess it's right to not use the tag when talking about Star Wars, for instance.

I guess too that The Wire's 5th season was enough years ago to don't use spoiler tags. I've learned this the hard way (Dexter 5th season finale, amongst others) and stopped worrying about this. It's the Internet, there will be spoilers no matter how careful you browse.

Again, the only thing I can think of where using spoiler tags was absolutely necessary is in unreleased shows/movies/narrative

By the way: Bruce Willis is dead.

Soylent green is people

Kaiser Soze is Kevin Spacey.

It's been 2 and a half years since the end of the wire. I don't think he owes you a warning