Posted to predict that an established meme will soon be posted in the thread, in the form of In before *. If the predicted meme is indeed posted, a reply of In after *. may follow. Slightly more rarely, the initial prediction may be replied to with In with *. or In during *. It can also be applied to tripfags who have predictable behavior and will often post in such thread that are relevant to their interest.
An alternative use of In before is to prevent future posters from posting that meme, since no one likes to look like an idiot.
In before Libertine
A meme used on chanchan during the time the pedophile who went by Libertine was posting. In order to start his grooming process, Libertine would comment on every loli's thread moments after she started posting.
The meme was also seen as in b4 lib.
- See: Libertine