Is it possible to mark entire threads as “read” even though I didn’t read them (I’ve seen this option before). If so, how do I do this?
at the bottom of the main page, there is a link ‘mark all threads as read’.
In other words, read all the threads that you want to read, skipping the ones you don’t want to read, and then mark all threads as read.
Thats what Ive been doing for ages. I have to say, it works. 
and here’s some insight as to how and when the icons all change, etc
…from the vBulletin support forums
Whenever you click on any part of the forum, vB starts a ‘timer’. If the next click occurs before the timeout setting, then a new timer is started and the new message icons stay ‘on’. If however there’s no new click until after the timeout setting, then the prvious messages will be considered read and the ‘on’ icons will only appear for messages posted since the last timer was set.
Is there a way to mark a single thread as having been read without marking all threads as having been read?
not that i know of.
i guess…click on the link, let the page load, don’t read it, then hit the back button would be the only way i can figure out … 
This thread was created 9 days before the day i was born… that’s pretty crazy… this thread is actually older than me! :ahh:
The crazier thing is that people who posted on this thread are still active on CD. There have been people who are still active on CD and have been posting longer than you have been alive.
Wow! This takes the cake for necroposting.