"Why don't you get out of those wet clothes and…

“Tales of Hoffman” by Irving Hoffman stated in The Hollywood Reporter (Hollywood, CA) on August 14, 1937:

“Someone recalled the following line of swell dialog the other day, but couldn’t remember where it came from. Perhaps you might know. ‘...I’d like to get out of these wet clothes and into a dry martini!’”

American humorist Robert Benchley (1889-1945) was written about in the syndicated newspaper column “In Hollywood” by Paul Harrison in September 1937:

“Hollywood. Sept. 9.—Short takes Robert Benchley had spent a long, wilting day under the hot lights on the ‘Live, Love and Learn’ set. He sighed, ‘Golly, it’ll be nice to get out of this wet suit and into a dry Martini!’”

The actor Charles Butterworth (1896-1946) said “You oughta get out of those wet clothes and into a dry martini” in the movie Every Day’s a Holiday (filmed in September 1937 and released December 18, 1937). Benchley used the line in the movie The Major and the Minor (1942).

Benchley is usually associated with the line, although he stated in 1942 that he’d read it in a joke book.

Wikipedia: Robert Benchley
Robert Charles Benchley (September 15, 1889 – November 21, 1945) was an American humorist best known for his work as a newspaper columnist and film actor. From his beginnings at the Harvard Lampoon while attending Harvard University, through his many years writing essays and articles for Vanity Fair and The New Yorker and his acclaimed short films, Benchley’s style of humor brought him respect and success during his life, from New York City and his peers at the Algonquin Round Table to contemporaries in the burgeoning film industry.

Wikipedia: Charles Butterworth (actor)
Charles Edward Butterworth (July 26, 1896 – June 13, 1946) was an American actor specializing in comedy roles, often in musicals.
(...)
He is credited with the quip “Why don’t you slip out of those wet clothes and into a dry martini?” from Every Day’s a Holiday.

14 August 1937, The Hollywood Reporter (Hollywood, CA), “Tales of Hoffman” by Irving Hoffman, pg. 3, col. 4:
Someone recalled the following line of swell dialog the other day, but couldn’t remember where it came from. Perhaps you might know. “...I’d like to get out of these wet clothes and into a dry martini!”
(No follow-up answer was printed.—ed.)

31 August 1937, Dallas (TX) Morning News, “Edmund Lowe Signed For Mae West Film,” sec. 1, pg. 12, col. 3:
HOLLYWOOD, Calif., Aug. 30.—Edmund Lowe today has been signed to play a leading role in the next Mae West starring film for Paramount, “Every Day’s a Holiday.” scheduled to go into production Sept. 8.
(The film Every Day’s a Holiday would open on December 18, 1937, so it’s unlikely that the line originated in the film.—ed.)

10 September 1937, The Daily News (Frederick, MD), “In Hollywood” by Paul Harrison (NEA Service Staff Correspondent), pg. 13, col. 3:
Hollywood. Sept. 9.—Short takes Robert Benchley had spent a long, wilting day under the hot lights on the “Live, Love and Learn” set. He sighed, “Golly, it’ll be nice to get out of this wet suit and into a dry Martini!”

1 February 1938, The Hollywood Reporter (Hollywood, CA), “Reviewpoints” by Irving Hoffman, pg. 2, col. 3:
(A review of the film Every Day’s a Holiday,—ed.)
Catlett’s sticker-pasting draws laughter, as well as the repetition of that old line, “Why don’t you get out of your wet clothes and into a dry Martini?”

19 September 1938, Kansas City (MO) Star, “About Town” by L. L., pg. 5A, col. 1:
Bob Benchley officially denied the line most widely attributed to him, that of a man hurrying into his club out of the pouring rain and telling his friends:

“I’ve got to get out of these wet clothes into a dry Martini.”

20 September 1937, Pittsburgh (PA) Press, “One Girl Chorus” by Aleen Wetstein, pg. 32, col. 6:
I LIKE WHAT Robert Benchley said one day on the lot when he finished the afternoon’s shooting, hot and tired. “Look, I’m wringing wet. I’ve got to get out of these wet clothes and into a dry martini.”

IMDb (The Internet Movie Database)
Live, Love and Learn (1937)
Passed | 1h 18min | Comedy | 29 October 1937 (USA)

IMDb (The Internet Movie Database)
Every Day’s a Holiday (1937)
1h 20min | Comedy | 18 December 1937 (USA)

7 June 1942, The Sun (Baltimore, MD),“Dry Martini Gag Hounds Benchley Down The Years” by Amy Porter, sec. 1, pg. 4:
New York.
It was a good joke when it was new. It’s still a pretty good joke, but Robert Benchley would rather not have any more truck with it.

“It never belonged to me in the first place,” said Benchley.

“I saw it in a joke book one day—this was out in Hollywood—and when I went to the studio I said to a fellow, “Say, here’s a pretty good one I found in a book, guy comes home in the rain and says “I’ll have to get out of these wet clothes and into a dry martini.’”

He Gets The Credit
“The fellow liked it, and he told it around here and there and that night somebody saw me and said, ‘Bob, that new line of yours is okay.’

“‘What line?’ I asked him, and he said, ‘you know—I’ll have to get out of these wet clothes and into a dry martini. Yes sir, that’s all right.”

“‘Oh that’s not mine,’ I said. ‘I read it in a book,’ I said. That’s what I said before witnesses.”

A couple of years later, when Bob Benchley had grown to such stature as an actor, author and master of wit that people wanted to know where he was born and did he go to school, which he didn’t any more than he could help, a magazine writer who was piecing together a piece about him asked:

“Can you please give me some good jokes of yours to quote in this piece?”

IMDb (The Internet Movie Database)
The Major and the Minor (1942)
Quotes
Mr. Osborne: Why don’t you get out of that wet coat and into a dry martini?

22 November 1945, Hartford (CT) Daily Courant, “Benchley, Humorist, Actor, Dies: Noted Writer, Movie Star, 56, Recently Completed Six Pictures” (AP), pg. 13, col. 2:
Hollywood legend credits him, despite his denials, with originating the saying: “How to get out of these wet clothes and into a dry martini.”

New York (NY) Times
‘Into a Dry Martini’
Published: July 24, 1994
To the Editor:

Regarding the origin of the line “Why don’t you get out of those wet clothes and into a dry martini?”, discussed by Sander Vanocur in “Benchley’s Martini” (letter, July 12), here is what I learned while researching “The Movie Dialogue Quiz Book”:

In “The Major and the Minor,” a 1942 movie, Robert Benchley says to Ginger Rogers, “Why don’t you get out of that wet coat and into a dry martini?” Although Billy Wilder was the movie’s co-writer and director, he said Benchley came up with the line.

Benchley, in his turn, attributed it to his friend Charles Butterworth. Indeed, in the 1937 “Every Day’s a Holiday” (starring and written by Mae West), Butterworth tells Charles Winninger, “You ought to get out of those wet clothes and into a dry martini.”
DIANE GIDDIS
New York, July 14, 1994

OCLC WorldCat record
I must get out of these wet clothes and into a dry martini
Author: Alexander Woollcott; Alan Stein
Publisher: Parry Sound : Church Street Press, 1997.
Edition/Format: Print book : English