Childish, Colloquial, Often Something that is forbidden, prohibited, discouraged or taboo.
Smoking indoors is becoming a real no-no these days, in many places.
Mr. UDALL. Madam Chairman, the gentleman from New York (Mr. Bingham), is wrong in his supposition that the use of a picture is to be prohibited on a newsletter. Let me make some legislative history. The masthead or the heading of a newsletter with a picture of the Member is intended to be approved. As a matter of fact, in this language we turned it around. These no-noes are taken out of the old Post Office Manual, where they had over the years compiled a list of things one could or could not do, and pictures, except to illustrate text, used to be under the prohibitions.1973, Franking Privilege for Members of Congress: Public Law 93-191 (Effective December 18, 1973): A Compilation of Legislative History, Washington, D.C.: U.S. Government Printing Office, page 63:
2 more examples
And a person of integrity observes all the good sportsmanship rules toward a beaten opponent. Integrity recognizes the integrity of other persons. To do otherwise would be to commit a no-no. And you don’t want to go around committing no-noes, do you?1975, William Nesmith, Congratulations, Graduate!, Thomas Nelson, Inc., →ISBN, page 62:
Countless issues arise in family life every day, from the litany of no-noes showered on the toddler, to calling the preschooler in for his lunch.1975, James H. Ryan, Pablum, Parents & Pandemonium: Glimpses of a Pediatrician’s World, New York, N.Y.: Thomas Y. Crowell Company, →ISBN, page 254: