I panic gym, you panic gym, we all panic gym. That situation when you spontaneously decide to go out/you're know you're getting laid later/other and you look in the mirror to find your muffin top staring back at you. 'Panic gymming' is a desperate attempt to reverse the damage when it's already too late.
'Why are you so late to pre-drinks, Stacey?'
'Oh, I was panic gymming.''