Kryptnit is a word meaning "fly or cool" mostly used by someone who would play a stupid game like w.o.w or something. Also, used when pissed off or angry at someone, but usually when angry at an object, if you say a person is kryptnit when angry your a douche.
"Dude, this is mad kryptnit"

or

"Kryptnit! God Dammit!"
by xMaddieeBeex March 12, 2009
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