watercooler effect
n. The effect created by two or more employees having an informal, face-to-face conversation, as though at a watercooler.
There also was the "watercooler effect," or the theory that people come up with their best ideas when grouped informally, said Jeff Wirt, president of the Pasadena, Calif.-based interior design firm Wirt Design Group, which planned open offices for several tech companies during the 1990s.
—Month Phan, “Breaking Down the Internal Barriers,” Newsday, January 10, 2002
1992 (earliest)
The MVP president attributed the success of HMOs in general to the "watercooler" effect — employees comparing insurance plans among themselves at work. "HMOs have been around long enough so that people feel they're OK," Oliker said. "When you can say you're getting value, people really respond to that."
—Tim Aurentz, “Local HMOs Tally Gains, Losses for Open Enrollment,” Capital District Business Review, March 16, 1992