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The process of masturbating all day long, due to a lack of anything better to do, or because you are procrastinating.
I just got in a new porn and decided to go on a masturthon, twas a good day.

My wife went on a marathon today, which gave me the opportunity to have a masturthon in the den with my trusty companion lupradeena.
by Yardstick&RichyDick July 07, 2011
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