It’s a pretty straightforward answer actually: one of those cases where when you see the steps between A and F, it makes sense.
Why is “Dick” Short for “Richard?”
dick
Don’t be such a…
You can imagine any word you like to finish that sentence. Personally, I’m thinking of a few different words. Words that all have two things in common: they can be used to insult a man, and refer to the male sexual organ (so be forewarned: if you’re sensitive to bad language, I’ll be swinging a lot of it round willy-nilly in the next few paragraphs).
English-Language Thoughts 