Never let them see you sweat! (Dry Idea commercial)

"Never let them see you sweat!" was coined by a "Dry Idea" deodorant commercial, one of which featured New York-based designer Donna Karan.

The phrase "no sweat" was popularized by the Korean War in the early 1950s, and the phrase "Don't sweat the small stuff" appeared soon thereafter.

17 November 1985, Washington Post, "Donna Karan's Dry Wit," pg. D1:
The person most surprised to learn her television commercial for the deodorant Dry Idea is being aired nationally is Donna Karan.
(...)
The commercial's story line, and Karan, is terrific. She gives "three nevers" in fashion design: "Never confuse fad with fashion. Never forget it's your name on every label. And, when you're showing your line to the press, never let them see you sweat."

In the second version, which hasn't aired yet, Karan added another savvy bit of advice for those starting their own business: "Never make dinner plans!"

(Trademark)
Word Mark NEVER LET THEM SEE YOU SWEAT
Goods and Services (CANCELLED) IC 003. US 051. G & S: DEODORANTS AND ANTI-PERSPIRANTS. FIRST USE: 19840607. FIRST USE IN COMMERCE: 19840607
Mark Drawing Code (1) TYPED DRAWING
Design Search Code
Serial Number 73710093
Filing Date February 8, 1988
Current Filing Basis 1A
Original Filing Basis 1A
Published for Opposition August 16, 1988
Registration Number 1511434
Registration Date November 8, 1988
Owner (REGISTRANT) GILLETTE COMPANY, THE CORPORATION DELAWARE PRUDENTIAL TOWER BUILDING BOSTON MASSACHUSETTS 02199
Attorney of Record JOY N. ELBAUM
Type of Mark TRADEMARK
Register PRINCIPAL
Live/Dead Indicator DEAD
Cancellation Date May 15, 1995