Top Definition
Obligatory pre-sleep wank. The required wank which occurs just before one goes to sleep, usually to aid in falling asleep. The OPSW is usually done with free internet pornography, including but not limited to the free tour feature on most sites, amateur pages, and pre-teen myspace profiles.
"Gonna go have an OPSW then sleep. Later."
by keithmoon December 14, 2008

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