Two entries in the 1811 Dictionary of the Vulgar Tongue:

Dick. That happened in the reign of the queen Dick, i.e.
never : said of any absurd old story. I am as queer as
Dick’s hatband ; that is, out of spirits, or don’t know what
ails me.

Dicked In The Knob. Silly. Crazed.

My guess is that someone who was being a jerk was “dicked in the knob”, which was shortened to “being a dick”, and even shorter as “a dick”.

Note Cole Porter’s lyrics from Kiss Me Kate, sung by Kate’s mad-to-marry sister, who wants

Any Tom, Dick or Harry,
Any Tom, Harry or Dick.

A dicka dick
A dicka dick.

What about thar Brittish tradition, Spotted Dick?

Welcome to the Straight Dope Message Boards, staev, glad to have you with us.

Funny you should mention that: What’s the origin of “spotted dick”? is today’s Staff Report. Thanks for the plug!

Interesting guess, but nothing to back it up.

“Dicked in the nob” is a stand-alone phrase from 1811. It appears in Lexicon Balatron.: “Dicked in the Nob. Silly. Crazed.”

It didn’t appear in Grose’s Classical Dictionary of the Vulgar Toungue. It wasn’t in the 1788 edition , nor the 1796.

It did appear in his 1811 work named as I entered above.

Of course it probably was in speech well before that date.

Not much in print to suggest that the 1811 phrase went on to become “being a dick.” What would one be who was being a “dick?” It’s possible that it could have meant “penis” in the early 1800’s, but not much to prove it.