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2.
When a male has fapped so much, that one arm is bigger than the other one.
Guy 1 "Dude how did Daniel get so buff?"

Guy 2 "Look at his arm."

Guy 2 "It's because he tones his Masturbation Muscle."

Daniel "No! I just workout."
by Lifewithaknife October 31, 2011
 
1.
A person who attains muscular definition or gain in the arms primarily through masturbation. One must not uniformly masturbate or masturbate solely with one arm if he is to achieve a significant or aesthetically pleasing result. Ways to fully utilise this workout include but are not limited to:
Set arm days
Switching arms halfway through masturbation
Freestyle (recommended for experienced users only)
''Wow your arms are so big you must workout loads!'' girl says flatteringly while feeling on arm.

''Not that much to be honest with you I'm just naturally endowed,'' typical lie said by happy user of MM method.

''Those are definitely masturbation muscles,'' murmurs a well-educated onlooker to his friend enviously.
by cheesyballs January 26, 2014