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Sometimes spelled bonerflex. A boner-flex is when one is in a public place or something and he is horny and has a boner. However, not wanting to embarrass himself by masturbating, he flexing his penal muscles to acquire the intended pleasure.

The word boner-flex can also be used as a substitute for various swear words.
Dude, I was so horny in class so I just had a great boner-flex.

Dude, what the boner-flex?!

Son of a boner-flex!
by Smittalicious October 21, 2014
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