no-no

[ noh-noh ]

/ ˈnoʊˌnoʊ /

anything that is forbidden or not advisable, as because of being improper or unsafe: If you want to lose weight, rich desserts are a no-no.

Origin of no-no

1940–45, Americanism; reduplication of no¹

Not all scientists agree that artificial sweeteners are a no-no when it comes to your health and diet.

Are Artificial Sweeteners Wrecking Your Diet? |DailyBurn |September 30, 2014 |DAILY BEAST
Converting at birth the children of non-Jewish mothers is now a no-no.

In Italy, a Traditional Jewish Lifestyle is Disappearing |Anna Momigliano |December 13, 2013 |DAILY BEAST
The point is, nobody knows what's next on the Hamas no-no list, which is almost always enforced before it is pronounced.

Hamas: The Palestinian Fashion Police |Hussein Ibish |April 9, 2013 |DAILY BEAST
Raising taxes is a no-no with Grover, so that leaves raising the eligibility age.

How to Make Seniors Suspicious of Ryan and Romney |Michael Tomasky |August 22, 2012 |DAILY BEAST

This is a no-no in the LDS church, to say the least, and as a result Scott spent a year or so “disfellowshipped” for his sins.

Turning Spotlight on Mitt Romney Siblings Could Help Humanize GOP Nominee |Michelle Cottle |May 30, 2012 |DAILY BEAST
"No-no; I thought of that myself, and Nemu too advised it," cried Ani.

Uarda, Complete |Georg Ebers
No-no, that won't do; you mustn't talk, and you mustn't retch and gag that way, either—you'll wake up your poor brother.

Those Extraordinary Twins |Mark Twain (Samuel Clemens)
They're going to take No-no home, then we're all going to the movies.

Ruggles of Red Gap |Harry Leon Wilson