How did "johnson" become slang for penis?

Don't know, I'm still trying to figure out "Shwang"

Maybe someone really didn't like their current President.

Years ago there was a guy called Mr. Johnson who was well known for his huge penis.

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.

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.

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.

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.

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 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 wondered if it had anything to do with "Doc Johnson," one of the first companies selling "love toys."

Actually plenty of slang names for penis are totally unrelated, like "tallywacker" for example.

Johnson was used in the first part of the 20th century in the underworld to refer to a penis. It was being used there long before LBJ or Don Johnson came around. The term "Johnson bar" referred to previously was known as a "Johnson rod" by safe crackers (yeggs) who used trains a lot for their getaways. The term "rod" for penis is quite old, dating back at least to the 19th century. "Johnson" became a clipped back version of "Johnson rod" sometime in the early 20th century. In a document written by a safecracker in the 1930's he uses the term. Ishmael Reed used "Johnson" for penis in his fiction in the 1960's when the term was no longer restricted to the underworld but was still pretty much restricted to urban argot. The term diffused to "mainstream" usage sometime in the 70's or 80's. Terms such as this one are often used within subcultures long before they diffuse to mainstream usage.

I'm thinking it came from the opera "The Girl of the Golden West" by Puccini (1905).

I'm thinking that the Johnson Bar in a train got its name from the euphemism, not the Johnson euphemism coming from the bar. I mean it stick up from the floor like a penis. I've heard its from LBJ and that's where my money is at. It's a very old term, could be from the Brits too.

I don't believe it could go as far back as the late 19th century. Reason being, there's an ad from the 70's for Johnson motors (boats) and the jingle sings, "You, your mate, and your Johnson."

If it was as prevalent as that, even the thickest of ad execs wouldn't make a commercial like that.

The first time I heard it in the media was in Top Gun. "The list is long and distinguished." "Yeah, so's my johnson."

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