Definition #1 To exercise solely for the purpose of flexing on people.

Definition #2 People who go to the gym just to run on the treadmill for 5 minutes, post a gym selfie then leave)
1. Dude Jenna’s at the gym, I’m gonna go Flexersize!

2. Gotta go Flexersize on snap (fake gym rat)
by urmom3.0 December 18, 2021
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When one goes to the gym and flexes in the mirror rather than actually working out.
ex

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 30, 2009
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