Doom_Blade97
Can no one post here I need the achievement.
Like the other poster says, it's gotta be in Chatterbox. But don't make it obvious you're gong for Invisibility, or they'll wreck it.
Try posting some really boring topic nobody would be interested in. Or try posting something trivial, like, "I just ate a sandwich," or "Just got home."
I got mine by making the thread title be the name of an item -- "Single Combat" -- that had been sold in the Cash Shop a few months before, that wasn't doing particularly well in the market. And I didn't give any information in the title, so if anybody even looked at it, they couldn't tell whether I was selling it or buying it or just interested in talking about it. If you are going to try this kind of strategy, remember, the less information in your title, the less attention it will get.
You can also bump the threads below you to push your own thread further down in the forum. The faster your thread falls, the better, because once it falls off of page 1, it gets a lot less likely anybody will post in it.
And good luck!