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When one goes to the gym and flexes in the mirror rather than actually working out.

Guy1 - wanna come to the gym with me?
Guy2 - no, go flexersize by yourself

ex 2

Andrew - Bro I just got back from the gym, got my swoll on.
Cory - Yea I saw you Flexersizing in the mirror.
Andrew - fuck you (walks away)
by cjtherriault July 29, 2009
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