English

Noun

rain man ‎(plural rain men)

1. (pejorative) An autistic, or mentally and/or socially impaired person.
2. (pejorative) A non-autistic or impaired person whose mannerisms are similar to such people.
3. (humorous) An expert at something. (Can we verify⁽⁺⁾ this sense?)
   • 2007, Kera Bolonik, In the Weeds, ISBN 1416938788, page 114:

     Lovingly dubbed the Rain Man of Weed by her family, Heylia James is legendary in West Adams for being able to "eyeball an ounce from outer space with her glasses cracked," and for making "everybody's business my business" ("You Can't Miss the Bear").

   • 2013, Jim Robbins, The Man Who Plants Trees, ISBN 1847659039:

     David Milarch calls him the “rain man of trees” because of his brilliance with tree data and his uncanny knack for finding the big ones.

   • 2013, Mike Doiron, Thread of Life: An Adoption Story, ISBN 147598216X, page 74:

     The mentorships were plenty, starting with Brian Derdall, a sort of rain-man genius in Engineering, along with T-man the technology guru, new hire peers Alex and Joel, and my new senior co-workers Ivan, Robert, and a sort of management mentor John.

Etymology 2

rain +‎ man

Noun

rain man ‎(plural rain men)

1. A man who is believed to have power to control the rain.
   • 1913, Walter Hutchinson, Customs of the World, ISBN 8172681704:

     The special relation between men and their totems is shown by a belief which exists in a large number of tribes, to the effect that the men have the power to make their own totem animal or plant increase in numbers; so that a kangaroo man can cause the kangaroos to multiply, a rain man can make rain, and so on. A kangaroo man cannot make rain, nor can a rain man do anything to increase the number of kangaroos.

   • 1978, William Tydeman, The Theatre in the Middle Ages, ISBN 0521293049:

     We believe that if we want rain, the rain man of the tribe must imitate the rain by squirting water from his mouth, and the painters must retrace the age-old paintings at the cave of the water totem.

   • 1995 November 7, Mike Foster, “Raindancer charged with manslaughter - after 7 die in flooding!”, in Weekly World News:

     As a huge crowd watched in anticipation, the 52-year-old rain man whooped and chanted while hopping about on a hillside.

   • 2005, Nathan C. Russell & ‎Simone Staiger-Rivas, Knowledge-sharing solutions for a CGIAR without boundaries, ISBN 9586940802, page 15:

     This is presumably because CIFOR used the services of a “rain man,” whose charges to keep rain away from Bogor for the evening were a small fraction of what it would have cost to hire a marquee.

2. A spirit of the rain.
   • 2009, Andrea Bandhauer & ‎Maria Veber, Migration and Cultural Contact: Germany and Australia, ISBN 1920898638, page 71:

     These depict in vivid descriptions how the rain man in the west expands in the form of a black cloud; white clouds precede him which unfold like a flower;

   • 2010, Garrett W. Cook, Renewing the Maya World: Expressive Culture in a Highland Town, ISBN 0292782519:

     In Santiago Atidán some saints' images are the embodiments of ancestral protective spirits called naguales — community founders, lightning men, mist men, rain men, earthquake men — who retreated to the mountains leaving the images and sacred bundles behind.