When you pull your dick out of a girl's ass(or guys) and the tip of your dick is dirty. Since the tip of your dick looks like Darth Vador's helmet, it is hence called a "Dirty Darth."
Guy1: So did you get some analriffic action last night?

Guy2: Yeah, I even got a dirty darth, but it's okay, I wiped it off on her upper lip giving her a dirty sanchez.
by JordanRichter September 14, 2006
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when at the end of anal sex, the tip of the penis is covered in feces.The tip of the penis looks like the head of Darth Vader thus the name, dirty darth.
man 1: hey, did you have sex with her last night?

man 2: yeah, but we did anal. It was ok but by the end I got a dirty darth.
by luke h-twig September 14, 2006
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when you take on the evil emperor so to save your son from dying and then banging your daughter with an invisible schlong
I've totally wanted to dirty darth vadar Stephanie but she won't let me.
by Dr. Simulacra October 24, 2013
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