it's a contraction of the words "must" and "have" but in the context of something being a "must have."
I'm going to get a pair of those New Balance 574s, they're a must've.
by snalker1 November 9, 2020
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A contraction of the words "must" and "have"
I must've left it some where.
by eleventhtoe October 22, 2011
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This sentence is often used when someone is acting unusually silly or crazy.

Originally refers to the roguelite roblox game Deepwoken. In-game it is said by one of the ignition union members after facing akira in the depths and being told to back off even though they outnumber him.
Ultimately ending in the squad's death after they pass the line drawn by akira.
A: "sticking out your gyat for the rizzler.. ur so skibidi.. ur so fanum tax"
B: "This one's sanity must've already crumbled..."
by r0lfu October 22, 2023
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