Of American-English origin, the noun neatnik designates a very tidy, well-organised person.

For example, the following is from Visual crusader, an interview of the British film director and producer Ridley Scott (born 1937) by Ciaran Carty, published in the Sunday Tribune (Dublin, County Dublin, Ireland) of Sunday 8^th May 2005:

Using multiple cameras and choreographing vast armies of extras, Scott has brought the same inventiveness and military precision to his movies, not just epics like Gladiator and now Kingdom of Heaven, but in eye-grabbing genre movies such as Black Rain. “I’m a neatnik,” he says. “I suppose getting things right is ingrained in the DNA. I always do my homework.”

A blend of the adjective neat and of the noun beatnik, neatnik originally occurred chiefly in contrast to beatnik, which designates a person who participated in a social movement of the 1950s and early 1960s which stressed artistic self-expression and the rejection of the mores of conventional society.

The earliest occurrences of the noun neatnik that I have found are as follows, in chronological order:

1-: From the Don Dedera’s column Good Morning!, published in The Arizona Republic (Phoenix, Arizona) of Sunday 15^th February 1959:

“START LIVING in 1965 today. Come back in 30 days and tell how you liked it.”
Needing stimulation for their firm, a couple of partners in a pioneer Arizona land company gave themselves that assignment a month ago.
[…] Here are highlights from their report:
[…]
Educational philosophy is changing, after a decade of critical self-analysis.
“Instead of giving courses which deal with adjustment to life, the schools are graduating students who are well-adjusted because they have a sense of achievement which comes from a challenge.”
“The neatniks have succeeded the beatniks.”
BUT THE CITY is breaking away from “the formal dress of the early 1960s.”

2-: From the column Good Morning From Claire MacMurray, published in the Cleveland Plain Dealer (Cleveland, Ohio) of Friday 3^rd April 1959:

I’m compelled to go on with the subject [of book lending and borrowing] because of a letter from Eugenia Thornton who is one of the best writers I know. […]
She says, in part, “Can you tolerate one more effusion re book borrowing? “I’ll try to divide it into sections like a neatnik.”

3-: From a television review by William Ewald, published in many U.S. newspapers on Thursday 16^th April 1959—for example in The Herald-News (Passaic, New Jersey):

NEW YORK (UPI)—[…] Last night, [Bob] Hope, working in loose alliance with Jack Benny and Ginger Rogers, bunched together a collection of taped sequences for a one-hour NBC-TV special. […]
There was even one Hope-Rogers spoof of neatniks that followed the pattern of a beatnik skit that Hope did with the wondrously plastic Carol Haney on a recent special.

4-: From the Pottstown Mercury (Pottstown, Pennsylvania) of Monday 27^th April 1959:

P. H. S. ¹ ALUMNI
Remember when the “Beatniks” Were the “Neatniks” And Nobody Was a Square ²?

¹ P. H. S.: Pottstown High School.
² square: a person considered to hold conventional or old-fashioned views.

5-: From the Los Angeles Times (Los Angeles, California) of Wednesday 6^th May 1959:

Female Beatniks Switch to Neatniks
BY PAT HERMAN

LONDON, May 5 (UPI)—There’s a revolution afoot in Chelsea, the bearded British beatnik’s answer to New York’s Greenwich Village and San Francisco’s waterfront haunts.
The girls have committed an unpardonable sin in the world of Bohemian bums—they have decided to beautify themselves.
[…]
[…] The girls, who used to bounce from bistro to bistro, their faces hidden by straggy [?] Brigitte Bardot-styled haircuts have broken one of the ground rules of the “Beat” cult. They have decided to clean themselves up—so much so, in fact, that their skin-tight leotards are now respectable enough for posh Mayfair.

6-: From Hayward Signs Up, by Louella O. Parsons, published in The Light (San Antonio, Texas) of Tuesday 12^th May 1959:

HOLLYWOOD—[…] I had a first-hand account of a species of juveniles in London, the English version of our American neatniks, from Cubby Broccoli, who is here from England for a few weeks. He told me his picture, “Jazz Boats,” which starts in June has to do with these characters who live under the Thames in caves and play nothing but rock ’n’ roll.
They wear miners’ caps and are as much a part of a strange new world as are our beatniks.

7-: From a UPI (United Press International) account of a meeting of the Red Feather Church-Welfare Institute in Montreal, Quebec, published in several U.S. newspapers on Friday 29^th May 1959—for example in the Bergen Evening Record (Hackensack, New Jersey):

Suburbanites Termed Neatniks; Even Religion Fits Into Place
Americans Consider Welfare In Sense Of Playgrounds, Minister Says

Montreal, May 29 (UPI)—A Presbyterian churchman yesterday condemned suburbanites as neatniks who have an overdeveloped sense of personal prosperity and a badly proportioned sense of welfare.
The criticism came from the Rev. J. C. McLelland, a professor at the Presbyterian College of Montreal, at a conference on social welfare planning in growing metropolitan areas.
Many suburban residents are members of a bourgeois society facing the dangers of middle-class economic virtues, he said.
“Suburbia’s idea of welfare will not involve any real engagement with its own area. Welfare seems to (the suburbanite) a kind of foreign mission effort, and touches his own community only in terms of playgrounds.”
Mr. McLelland said he regarded suburbanites as the neatnik generation because everything, including religion, fits nicely into place for them.
He said that as a class, they are people who cannot agree on whether to provide a swimming pool or skating rink for their community and compromise by buying a new car.