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A kick-ass abbreviation for the words: "spontaneous boner". If you're a rocket scientist, this means that the penis will become erect for no apparent reason.

See Morning Wood or Afternoon Wood.
Jack to John: "I have a spon-bon..."

John: "You know what I do? I flip my boner up into my waistband. It hides it AND it feels awesome. Once, I almost blew a load into my bellybutton."

Jack: "Shit! Don't have time!"

Hannah: "Jack, is that a banana in your pocket, or are you just happy to see me?"
by JordanAnderson September 08, 2010
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