Generally used on internet forums, inb4 refers to a user posting a reply to a message/topic "before" another user posts an obvious response. When used appropriately, inb4 is followed by a word or short phrase that the user knows will eventually appear in the topic conversation.
Jonny113: Jiraiya would beat the crap out of Itachi.

Steven387: inb4MS

Mike128: You know Itachi has MS, so Jiraiya doesn't stand a chance.
by CM Joker January 17, 2009
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An internet term that is short for "in before" used when someone replies to something before something that they anticipate to happen eventually happens.
by OoftheDoof! July 19, 2021
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You are calling something, you bet that it will happen.
inb4 a nerd said this to you
by Womaniser November 30, 2015
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a 4chan phrase that means "in thread before (b4) it 404's (gets deleted (you get a 404 error message when a thread is deleted))
"Anybody got some CP?"
"inb4 404"
by Vermin Supreme January 3, 2009
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Started on MLPForums, this refers to posting in a topic before ghostfacekiller39 that speaks badly of the character Rarity from My Little Pony: Friendship is Magic. ghostfacekiller39 is perhaps the most dedicated Rarity fan on the forums, and he's always quick to defend her when the need arises.
RarityHater69: "Rarity is the worst pony ever, she's such a bitch I hate her!"

GenericName123: "inb4 ghostie"

ghostfacekiller39: "(Long profound rant about why OP is wrong, with lots of Rarity smiley faces mixed in)"
by Frostgage March 6, 2014
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