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A person who breaks the Sixth Commandment which signifies the person slept with a married person.
"Oh shit! He just pulled a Seis"

High five for scoring with a married chick man!
by Seis716 July 20, 2010
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Sep 6 Word of the Day
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Damn that was a steezy ass kickflip son!
by niggaliciouszor April 29, 2007
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To be incredibly epic at basically everything. Seems to be from a different dimension, though this is up for debate. Will not admit to having ninja skills even though said skills are witnessed regularly. Prone to anime-type reactions (aka loud and obvious), usually ending in some form of destruction.
Person 1: WTF happened in here!? All the desks and chairs are destroyed!!
Person 2: Someone pissed off (insert random name here).
Person: What an idiot, everyone knows (insert random name again) is a Sei.
by Kiri :D June 20, 2010
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After that golden shower, those Russian hookers gave Trump good SEI even with their limited English: Open. Chew. Swallow. Eat it!
by urbanjungler January 15, 2018
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Every bad quality you can name.
Hawk is posting pictures that are depressing, and won’t y’all about it. He is being a sei.
by Randomposter333 March 17, 2018
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