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1.
The moment someone realizes that they got owned.
John felt he was up for the cinnamon challenge, but experienced plexus when he found that someone had replaced the cinnamon with cayenne pepper powder.
by abradacabra February 12, 2010
 
2.
(noun) a confusing or badly written legal opinion or contract

origin: late 15th century (as the adjective perplexed): from the obsolete adjective perplex ‘bewildered’, from Latin perplexus 'entangled', based on plexus 'interwoven', from the verb plectere
this memorandum is utter plexus
by Lord Wolff June 02, 2011
 
3.
the back of the knee
Alex rubbed my plexus and i felt so good.
by ur lover April 24, 2006