How do you delete these?

How?

Oh, thanks!

Basically, you can't delete them, but most people, when they have a thread that's no longer relevant, they put something like, "Ignore This" in the title, so that people know not to click on it. Sometimes, threads just become inactive, (we refer to it as "dying" or "dead thread") so that may be why you don't see some certain threads around anymore :)