It's offensive. Dick Grayson is a well - known character, and we should focus on his positive aspects like his heroism, his relationships in a non - vulgar way, and his role in the fictional universe. Using such a description not only shows disrespect to the character but also to the fans who appreciate the character for more positive reasons.
If we consider the Dickens - like interpretation from before, a big story could be 'A Tale of Two Cities' by Charles Dickens. It's a large and complex story that has many characters and themes. But this is really stretching the original, rather strange phrase.
I don't have a specific 'big dick friend story' myself. But it could be a story about a friend who is very confident, and people might associate that confidence with a certain 'big' personality trait, like being bold or having big dreams, rather than a literal meaning. It could also be a humorous inside - joke - like story among friends.
Since I don't know what exactly 'big dick lush stories' are supposed to be, I'm unable to share one. It might be some sort of inside joke or a very local form of storytelling that hasn't reached a broader audience.