inb4 is a common phrase used to stop people from saying things ahead of time. It means in before, which says that that poster has said the word before the rest of CE will, in a way. Sometimes, the word inafter is used, after someone has said inb4.
If the opening post of the topic contains an inb4, someone will usually say "TC can't inb4" unless the opening post also says "inb4tccan'tinb4".
TC: Fossil is stupid, he should be banned User1: inb4B7! User2: Oh you're gonna get banned ban. [TC is banned by Fossil] User3: inafterB7!
TC: Do i look good in these pics? [pictures] inb4ugly inb4notagirl inb4TCcan'tinb4 User1: inafternotagirl.