The term human bean is a humorous alteration or mispronunciation of human being, frequently used as part of an extended pun relating to beans.

It is first recorded in Punch, or The London Charivari (1842):

This little wretch is exciting the most intense interest, (Faugh!) and we have bribed the authorities in all directions to obtain information regarding him.
It appears that Bean was the son of his mother, but we have been unable to get from either of the parents the exact date when the vagabond was weaned, but we have drawn our own conclusions on the subject.
Since Bean has been in prison he has observed a sullen indifference, but he continues to eat and drink with appetite. It is a curious fact that when Policemen O. P. Q. asked him what could induce him to fire at the Queen, he placed the end of his thumb on the point of his nose; and as several boys have been observed to do the same thing, it is very reasonably inferred that Bean belongs to some secret society, of which the mystic symbol above described is one of the modes of communication between the members of the fraternity. The policeman sought an interview with Sir James Graham; and on being asked by the home secretary what he had to communicate, placed his thumb upon his nose, which had rather an odd effect until an explanation was given. Sir J. Graham remained some time in deliberation on the act reported by the policeman, and it was resolved that a member of the British Association should be called upon to give an interpretation of the mystic symbol.
The general opinion as to the punishment of Bean is, that a good thrashing, which is often applied to vegetable Beans with effect, may be resorted to in the case of this ordinary human Bean with the best result possible.

The following is from The Yorkshire Post of 3^rd November 1934:

A Dog’s Verdict
The children of West Riding schools have been at work writing essays on the following subject:—“A cat or dog describes the people with whom it lives.” A harmless subject, you might imagine: nevertheless it provided an opportunity for the West Riding essayists to get in one or two shrewd thrusts at authority.
[…]
A lot of the essayists headed their compositions, “A Dog’s Life,” which, I take it, was another subtle hint as to their feelings, and one expressed a wish to go to a “Crammer School.” Another described man, with biting irony, as a “human bean”—a variation on Carlyle’s description of him as a forked radish.

(In The Hero as Man of Letters. Johnson, Rousseau, Burns (19^th May 1840), the Scottish historian and political philosopher Thomas Carlyle (1795-1881) wrote “Strip your Louis Quatorze of his king-gear, and there is left nothing but a poor forked radish with a head fantastically carved”.)

The Science News Letter (Washington, D.C) of 2^nd March 1935 had:

The only guarantee of the worth of an individual for the breeding of a superior race is not its own superiority, but the superiority of its progeny, and this is just as true of the human “bean”  as of the vegetable bean about which the statement was originally made.

But it was the British writer Roald Dahl (1916-90) who popularised human bean in The BFG (Big Friendly Giant – 1982):

“As I am saying,” the Giant went on, “all human beans is having different flavours. Human beans from Panama is tasting very strong of hats.” “Why hats?” Sophie said.
“You is not very clever,” the Giant said, moving his great ears in and out. “I thought all human beans is full of brains, but your head is emptier than a bundongle.”
“Do you like vegetables?” Sophie asked, hoping to steer the conversation towards a slightly less dangerous kind of food.
“You is trying to change the subject,” the Giant said sternly. “We is having an interesting babblement about the taste of the human bean. The human bean is not a vegetable.”
“Oh, but the bean is a vegetable,” Sophie said. “Not the human bean,” the Giant said. “The human bean has two legs and a vegetable has no legs at all.”