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1.
It is what you call your nipples when they get hard.
Friend: dude, your nipples are hard.
Me: how about that, I'm nerpin.
by Dizymay_93 November 26, 2009
 
2.
When you're so extremely tired that you begin to get loopy.
Oooh mannn I'm nerpin', I should probably sleep or I might do something bizarre.
by Milkywayyyyyy December 10, 2010