A cross between the video game Fortnite and the mental condition Autism. This refers to those fuckers that practice synchronizing the hype emote or orange justice in the courtyard, then present it at the talent show.

Can also be used as Fortistic
The level of fortism at my work space is insane, no one wants to see your fucking synchronized orange justice guys, just get back to work!
by SomeBoiOnUD November 5, 2018
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A deadly mental illness which causes innocent kids to be a virgin forever

also a close relative to the word Fortistic
Kyle: DUDE! I got laid yesterday! How about u?
George: soz dude but I have Fortism
by ($0$) September 10, 2018
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A kid, typically between 8-14, who plays Fortnite: Battle Royale. They become particularly fortistic while playing.
"Look we got another twelvie on here."
"Yeah bring on the fortism aye."
by Sicko_sheila July 1, 2018
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