Why Do We Use This Expression?

My lady Jennifer asked about a widely-used term of disparagement: a real dick.

Now the word used in this sense can literally refer to the penis. And, furthermore, why would alluding someone to be a penis be disparaging? After all, approximately 50% (more or less) of people possess such features. And females supposedly enjoy their being used properly (or many men are credulous). So why is calling one a "dick" a put-down?

Could it be due to Richard Milhous Nixon, known as "Tricky Dick"? Unless he possessed a remarkable talent well-known but since forgotten from that strange time, I doubt it.

Actually, Eric Partridge in one of his works on slang recorded that reference to the penis as far back as the 1880s.

And there's the allusion of "shaking hands with the girlfriend's best friend."

But the British have a dessert of fruit and suet called "spotted dick." And they're not referring to Mr. Cheney or Mr. Nixon with measles. Some have even suggested calling it "spotted richard" instead.

I tried it. It wasn't bad.