Sugary Malice

Sure it Tastes Like Diabetes. But wait, what's that aftertaste? Cyanide?

Put simply: character behavior which looks or sounds sweet but is just as hurtful and cruel as a direct attack -- perhaps more.

Characters such as Magnificent Bastard, Devil in Plain Sight, Enfant Terrible, Deliberately Cute Child, and Bitch in Sheep's Clothing are all likely to pull off acts of Sugary Malice. A Wounded Gazelle Gambit is in itself merely malicious, but the fake victim can make it sugary by for example gently "forgiving" the "abuser".

A character who is Obliviously Evil, Totalitarian Utilitarian, Principles Zealot, Well-Intentioned Extremist or similar might also pull off this kind of behaviour -- sometimes without even realizing that his actions are in fact malicious. Such characters might cheerfully murder innocents, figuring that they have a good reason for doing it -- maybe that the good outweighs the bad or even that their victims are better off dead. Or they might play Black Comedy Rape or Romanticized Abuse in some misguided belief that it is okay... maybe inspired by a Marital Rape License or a Scary Amoral Religion. However, in any case, the characters must understand that their actions are abuse or murder or whatever it is they are doing, and still actively choose to do it, otherwise it's Obliviously Evil, not Sugary Malice.

Compare Faux Affably Evil.

Film

 * Arsenic and Old Lace is based upon the fact that a certain pair of sweet old ladies are inviting gentlemen over to drink homemade wine and then poisoning them.
 * In Never Let Me Go, Ruth has a bit of this, fueled by her fear of being left alone. Far worse, however, is the polite kindness that the system show it's victims while pushing them down into despair and death.
 * The Camp Chippewah counselors in Addams Family Values actually seem to enjoy tormenting Wednesday, Pugsley, and the other "weird" kids like this.

Literature

 * James H Schmitz's Telzey Amberdon short story "Novice". Telzey's Aunt Halet cloaked her malicious intent behind a pleasant façade.
 * In Harry Potter and The Order of The Phoenix, Dolores Umbridge tortures students -- but she's very polite about it, in a grandmotherly way. And just LOOK at all those cute little kittens!

Live Action TV

 * Everybody Loves Raymond. Marie often made insulting comments to Debra while pretending to give friendly advice...though Debra increasingly began employing it as well. However, when it came to her interactions with Ray, Debra delivered the malice sugar-free.
 * In the The Man From UNCLE episode "The Gazebo in the Maze Affair", the villain's wife, Edith Partridge, initially appears to be a sweet, if not-entirely-there, old lady who is oblivious to her husband's evil. It soon becomes apparent that she's pulling many of the strings, and she tortures the heroes -- and gives her husband instructions on how to torture them "properly" -- without ever changing her sweet manner.
 * Anna in V is pretty much the poster child for this. So sweet and innocent. And of course she is of peace, always. Even when she incites civil unrest, has people tortured to death and generally plots the destruction of mankind. Especially when she does those things.

Theater

 * While characterization may vary between directors, Arsenic and Old Lace often follows this trope in the same way as the film version does.

Western Animation

 * Mother May-Eye from Teen Titans, a Reality Warper with a side-order of mind-control, is by far the scariest of all the villains the Titans faced (not that it's an area of great competition).
 * Daemon from Re Boot, though she honestly doesn't see her actions as malicious.