It originated from the name of the male reproductive organ. It is the same shape and in some cases it is probably the size of yours if you are a guy reading this. Don't get fooled by pen and penis. Don't forget to put a space after pen when it is followed by the verb is, otherwise you would have spelt penis. See exemple below.
That pen is miniscular.
The only weapon on Earth mightier than the sword.
yo homie yo goin to the pen fool
pen is a abbreviation of Penitentiary ,
the Penitentiary is a prison , jail
i aint goin back to da pen
im not going back to prison
Noun: A small, hollow, ink filled object which disperses said ink onto various writing mediums, like paper, cocktail napkins, or anything suitably porous.
Hand me that pen, I need to jot down a phone number.
A prison, penitentiary, or correctional facility is a place in which individuals are physically confined or interned and usually deprived of a range of personal freedoms. Prisons are conventionally institutions which form part of the criminal justice system of a country, such that imprisonment or incarceration is the legal penalty that may be imposed by the state for the commission of a crime.
What can we do when we're arrested, but open fire
Life in the pen ain't for me, cause I'd rather die - Tupac
badly spelt and pronounced penis
I write with pens
2.chicken or animal enclosure
3.ABRIVIATION FOR PITTSBURGH PENGUINS