Cypress Hill! Ha ha! Remember, like I said, just sigh and move on here. This achievement means you've raised your reputation with the 8 most useless factions in the game. This is how factions work:
(1) Blizzard installs them as an official faction in the game, which means they get a name and a little progress bar in your reputations page.
(2) Blizzard implements some things you can do to improve that reputation, like quests, or items you can turn in, or something.
(3) Blizzard creates rewards that you get for having a certain reputation level, and puts a quartermaster in the game you can buy these rewards from.
There are a few factions in the game where they basically got to step 1, then when it came to step 2, implemented one thing you could do to increase that reputation, and then forgot about adding any more, and just really never got around to step 3 at all. So the lack of attention to step 2 means you can only increase your reputation at a snail's pace for those factions, and the lack of a step 3 means you get nothing for doing it except people shaking their heads sadly at you.
So the developers thought it would be funny to give out an achievement for getting max reputation with all of these factions, which one person has calculated would take approximately 360 hours of playing time, time that can't be spent killing bosses, getting gear, or achieving any game goals, never mind time you could spend with your family or exercising.
In return, not only do you get the achievement, but also a title that can appear at the end of your name.
So yeah, totally worth it.
Back in about 2005-2006, they introduced a new zone, Ahn'Qiraj, and were determined to make every single player appreciate all the work they had put into it by making it a pain in the ass to open.
First, the entire server, tens of thousands of players, Alliance and Horde, had to gather tons of random items for the "war effort," including bits of cloth, scraps of leather, random fish, and a ton of things suspiciously similar to what you find in hoarders' houses.
While the peons of the world were doing that, the top guilds were racing in their own way to become the official gate-openers.
They first had to pick an official ribbon-cutter in the guild to put all their efforts behind, and went on a crazy quest line involving clearing dungeons, killing bosses, going on scavenger hunts, and gathering 16,800 items dropped by monsters that players couldn't kill alone.
One down, 16,799 to go.
Whole guilds would spend days killing those 16,800 creatures and handing the loot to their designated star player, who, at the end of all this, would get the key, which was a scepter, because you know, fantasy world.
Once the whole server finished hoarding enough "war effort" items, and at least one person had a scepter, that person would go open the gate, and often enough, crash the server thanks to the ton of looky-loos gathered to see the event.
The gate-opener would then get the title Scarab Lord, as would anyone else who happened to have the scepter and was able to go click the gate within 10 hours of the opening without getting caught up in the server crashing, which considering the incredible timing needed, was usually nobody else.
So getting the title means you can walk around cities with people whispering to each other, "That guy is a Scarab Lord. There's only like one per server!" and then some of those people might care.
The rest of us just go, "Oh, that's interesting," and then go have sex.