Nigger Dick is used in replacement for "Fuck", or "Shit". Its more creative and will get a laugh due to its randomness.
Because when you think of Nigger Dick, you picture a big,
black hairy Penis.
By the way,
don't say it in front of a African American person...unless they know the just, they are from the Bahamas or you REALLY wanna get your ass kicked by some
guy named Tyron.