An acronym for Shit I Don't Need, aka junk or useless stuff. Pronounced SID-din. Usually used for boating toys and extra things no one will ever really need.
"Hey man, did you buy some SIDN yesterday?"
"Yeah dude! I know I don't need it, but it's fun shit!"
"What'd you buy?!"
"An anchor loop, three water chairs, coasters with extra grip, the third season DVD of Big Bang Theory, and a cookbook for potatoes!"
"Dude that's some serious SIDN!"
by lawlzop September 3, 2011
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