Tout sucre, tout miel
Tout sucre tout miel sounds like it could start a perfectly authentic holiday baking recipe. What could go wrong with “all sugar all honey,” if you mix it with equal parts of butter and flour? A sugar overload, maybe? Precisely. A person who is referred to as being all sugar all honey exhibits an extremely sweet and polite, even servile, behavior - indeed so much so that it looks somewhat suspicious as well as cloying. The expression is used ironically, to point out that the overtly affable person hides something behind the (fake) smiles: a character trait, or an agenda, that one perhaps would not want to admit.
The English expression to be all sweetness and light is almost equivalent, since it is often (though not exclusively) used in a negative or ironic sense too. Otherwise, getting away from the sugar idea, two-faced might also fit, if the context is right.
You may also hear the adjective mielleux with the same negative connotation, to describe someone whose behavior is exceedingly and insincerely sweet.
This idiom appeared in the 17th century, at a time when honey was rare, and regarded as the ultimate treat in the candy department, one that only wealthy people could afford. It was the very symbol of sweetness. Tout sucre tout miel relies on the idea that sugar and honey are, well, sweet to start with, and that combining both is going to be overwhelming for your tastebuds - not to mention your pancreas. What bitterness is the cook trying to conceal with so much sweetness?
To understand the full extent of the expression, one should remember that 300 years ago, our ancestors ate about 1 pound of sugar per year, per person, at best. Today, when the average person eats well over 50 pounds of added sugar per year, no one would frown over a little honey mixed with sugar. Hot fudge cookie 'n cream caramel freakshake, anyone?
Quand ils ont des invités, elle est tout sucre tout miel, mais dès qu’ils sont seuls, elle est odieuse avec lui.
When they have company, she’s all sweet, but as soon as they’re alone, she’s nasty with him.
Pierre était tout sucre tout miel aujourd'hui; je me demande bien pourquoi. Ce n'est pas dans ses habitudes.
Pierre was all sweetness and light today; I wonder why. This is out of character for him.
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