If you can't access the site, you have a minor freak out - and a major case of hitting reload. (I usually wind up on the LJ Support IRC channel to get the freshest news, which also gives me something else to do while the site's down.)
You found yourself composing journal entries during dates, movies, even sex!
When you're out, you suddenly think of a witty reply to a comment somebody made to you...several days ago.
You actually call it LJ and not Livejournal.
You've downloaded some sort of LJ program which has only the purpose of making entries easier to write without going on the site manually.
You have more friends on LJ than in real life. (Except that many of my LJ friends I'd call friends face-to-face as well, but I do have more people I read/readers than I have friends.)
You can't seem to call your friends by their real names - only LJ names will do. (In general, most of the people I hang with tend to have their own names. Whether their name-of-choice is their birth-name or not is another story. Sometimes it coincides with LJ name, sometimes it doesn't.)
You've fallen in love with someone you met on LJ.
You have posted about a party or get together on your LJ...
You are guilty of traveling more than an hour to meet someone with LiveJournal. (Note the above-mentioned love/girlfriend thing.)
You've written a protected entry about one of your LiveJournal friends.
You have written posts to notify people you're going to sleep.
You talk about your LJ friends to your real life friends all the time... like they're a part of your group. (Because they are part of our group. Just not a local part. Except for the cases where they are local.)
You've created a LJ community, and people actually post in it.
You've been recognized in real life by a fellow LJ'er. (Sort of. We thought we'd met on LJ, but no. Oh, wait, there was that friend of reichiere's who saw me in lab...)
You have friended someone because of their LiveJournal icon. (I know I have, but I can't recall who all.)
You have "pity friends" on your list, who you would defriend if you could. (Very few.)
You've pimped one of your friends on journal, trying to get people to friend him / her.
Instead of doing research, you post difficult questions on your LiveJournal.
Your pets all have their own LiveJournals.
You know, right now, how many people have friended you (without peeking).
You've stopped being friends with someone in real life because of something they've said on LJ.
You're guilty of posting sexy or nude pictures to get more people to friend you.
You have consoled yourself after a horrible day thinking "At least this will make a great LJ post"
You're jealous of people who have more friends and / or comments than you.
You have written a really great, solid post - only to be disappointed by the lack of good comments.
You're guilty of commenting excessively to get more traffic to your journal.
You've deleted a post a few minutes (or hours) after you've written it, because it seemed lame in retrospect. (Actually, I just take them private.)
You give shout outs to all your LJ friends on their birthdays. (Sometimes.)
You have an additional, secret journal that hardly anyone knows about.
You have gotten mean anonymous comments (bonus points for figuring out who it was via their IP) (Idiot had left comments under his ID in the same day, hello matchup, especially because it was a Bitter Ex, but one who's safely married now.)
You've been reported (or reported someone) to LJ Abuse. (Spaaaaaaammers.)
You've been featured on LJ Drama. (I was involved in a Fandom Scruples fufurrah.)
(some new ones)
You become confused when two or more of your friends have the same icon. (Bonus points if you have seen the faces of these people.)
You introduce yourself face-to-face by your LJ name, not the name on your ID. (Unless, of course, one's got the same name for LJ and on ID...)
You actually get these jokes and pass them on to other friends who are LJ addicts.