Johnson is a popular term for the penis- made all the more popular by the infamous "Big Johnson" t-shirts. There is some speculation, but little hard evidence as to the etymology of the word.

Here are some of the possible origins:

* There is a town in Indiana called "Dick Johnson". It's not hard to get the association here.

* It is perhaps related to British slang John Thomas, which had the same meaning around 1863.

* R. G. Johnson made baseball bats in his Sebago Bat Company. He always burned 'R. G. Johnson' into his bats. The bats were referred to as "Johnson's" and since the penis somewhat resembles a baseball bat it might have been used as a euphemism.

I don't know, but I was disappointed when I found this out a yr. ago b/c I got a dog from the humane society named Johnson and I was going to keep that name until I found out what it was slang for. lol

I also saw the History Channel program about steam trains and noticed the reference to "Johnson bar" to control the speed. I agree with the earlier post that this is most likely how the term "Johnson" came to refer to a penis. The "Johnson bar" is long and sticks out horizonally.

President Johnson (LBJ) was proud of his junk and spoke about it often to his buddies. This info made its way from his inner circle into popular culture.

On the History Channel ("Marvelous Marvels") on Friday night, they featured the old steam locomotives...it showed an engineer in the cab, and to control the speed and direction of the train, he grabbed a long, round, brass lever, protruding from the floor of the cab...The narrator referred to it as "the Johnson Bar"..
Mystery solved.

I always heard it was because Don Johnson has a big one and that's how it got known around Hollywood. I have actually seen evidence of this and it is true, it is big. Those T-shirts in the other answer came out way after this slang started being used so I don't think that is the answer.

My money is on Don.

I didn't know it was. Are you sure about this?