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When the mentality of one member of a group cause the rest of the group to follow suit. The behaviour shown is usually anti-social, brutal and mob-like.

A perfect example is in the film Stoic, staring Edward Furlong. 3 guys in a prison cell fall into the same mindset, playing off each other, and torment, rape and torture their 4th cell mate, leading to his suicide.
Guy 1 "I think we should bum Guy 3 ragged."
Guy 2 "I dunno man, that's not right"
*Guy 1 starts bumming Guy 3*
*Guy 2 joins in and skull fucks Guy 3*
Guy 3 "So this is group psychosis?! How fun! Let's swap ends!!*
by Jam_1_ January 06, 2014
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