This words stems from the guy named Harold on the movie "Kids". It's where you pull down your pants and start slapping your semi-hard penis back and forth off each leg. You can also use it during sex while your cumming, slapping the girl in the face.
I whipped out my dick at the party and did the Dirty Harold!
by Smitty,E September 23, 2006
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A reference to Harold Ramis, the actor who played Egon in Ghostbusters, the act of you (Harold) swinging your balls an inch above your friend's face while he sleeps as you chant "I ain't 'fraid of no ghost" repeatedly until he wakes.

A bonus would be the friend waking up with his first reaction to lift up his head which would ram into Harold's dangling/swinging nards which is when Harold must respond with, "he slimed me".
As Nic was sleeping, Carey pulled down his pants, squatted over his face and gave Nic a Dirty Harold

OMG, look at Stu giving Sam a Dirty Harold
by Beardiful January 14, 2013
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when your hanging out with your friends and you get bored so you strip to your underwear and start grinding on them, turning them on and eventually you all have a big gang bang but with spicy twist, you and your friends put taco powder on eachothers dicks and smack eachother while calling eachother juan
last night i did the dirty harold with my boi gage, Russell, and julian rodierojomcde
by Gotm_oof November 16, 2017
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Doing a chick in the ass while she eats a White Castle Burger then pulling ur dick out and wiping it on her burger and saying "Thats how NPH rolls!"
White Castle sucks balls. They need shit on their burgers to taste better. Improve the taste of their burgers with a Dirty Harold and Kumar.
by ~Valhalla~ February 16, 2007
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