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1.
A Jumping-Jack Off is just like the motion of jumping jacks, except you have one hand in that particular motion
I went to the gym, and as a joke I did my entire work out. The very last one I started the Jumping Jack-offs

The best way to loose weight is to do Jumping Jack-offs
by Cadillac C--Y February 09, 2011
 
2.
The act of masturbation during jumping jacks, usually performed by alternating hands each jump.
Guy 1: Why didn't you go to the gym yesterday? You're going to get fat.
Guy 2: No I'm not, I stayed at home and did jumping jackoffs. I was so tired afterward.
by Iforgot911 January 10, 2009