Just make a sentence with "You know you're <something> when..." and that's it.  Just like in Categories, put the <something> in the post Subject line.  The subject stays until someone changes it.

Example:

Subject: You Know You're A Nerd When...
Post: ...When you want to be a 17 year old back in the 80's

You know you're a nerd when you watch obscure movies and TV shows that nobody ever heard of, and you end up laughing at your own jokes about them because nobody else knows what you're talking about.
This message was last edited by the player at 14:06, Fri 05 Feb 2010.

When you can draw the caffeine molecule from memory.

You know that Double Meat is a Buffy reference.

You fail to read the rules of a game!

When you point out that people can't read the rules.

When you complain about having to change subjects back over and over again.

when you have yet to get layed, and you're forty and not a Eunuch.

...you can quote Revenge of the Nerds verbatim without a sense of irony.

You've been to 4 Weird Al concerts and can sing along to all of his songs.

You have serious conversations with people you just met about Star Trek, having no prior knowledge of whether or not they watch(ed) the show(s).

You would rather play Red Dead Redemption than go on a date.

You argue with your friends about the politics of Azeroth and the merits of forming the Alliance in the First War and whether the alignment of Kalimdor today might be better or worse if the Horde hadn't come at all, how much influence the Nightmare really has on the land of the waking, whether Nozdormu's brood will play much more of a role in Cataclysm, and what the best strategies are for the Lich King fight.

... you refer to your friends by their gamertags and internet screen names.

When every piece of tech you own has earned a VESA sticker.

... you read someone say all of their tech has earned a VESA sticker, and you can't be bothered to Google VESA to find out what that is.

... the remote is right beside you and you command someone to turn the channel.

When you have a mural of Brian Bendis on your wall. And because I can almost guarantee that you dont have one, and that you probably havent seen one, yes. It is ten times more art-worthy than the mona lisa. Best part is, it only cost me $599.99.

...you briefly consider looking up VESA, Brian Bendis, Mona Lisa, murals, Google, and the current value of the dollar in order to make a sarky response, but you can't bother to use a keyboard or a mouse.

You drink liquid Krispy Kremes cause chewing is too much work.

When you cry when you're mother gives away you're complete batman figurine collection to an irresponsible, eight year old cousin when you go away to college. That collection would be worth well over $1,500.00 if it wasnt chewed apart by a slew of mindless idiots. In the December of my senior year of highschool I had an appraisal done, and the entire set [including the galvanized alloy batmobile] was worth 1,200.00, and things like this only increase in demand. Not that I would have sold them. Though I'd still rather have the money than nothing at all.

... you read they make liquid Krispy Kremes and think that's the best idea ever, but are still not likely to find out if it's true and where one might procure such a tasty beverage because that sounds like work.