Lakritze has suggested the word to sneer for this blog. I agree, it is worth looking into, so I will try. To sneer is defined in English as a look of haughty disdain, scorn and/or disgust expressed by smiling in a conptemtuous way. It is used both as a verb and as a substantive, the substantive being in my opinion more difficult to translate into German or Spanish in a succint way.
It seems to be a very English expression of superiority, although while sneering one does not keep a stiff upper lip, but has to curve it obliquely instead. Americans, it seems, are not so good at it, they even say in their dictionaries that to sneer is
to speak in an unpleasant way that shows you do not respect someone or something and you think you are better than them
I think real Englishpeople do not have to speak to sneer, they just use a gesture related to a snarl. I can even imagine an Englishman like, say, Mr. Boris Johnson, looking at his reflection in the mirror and sneering with delightful haughtiness at himself unaware of the contradiction, but that probably just goes to show that I do not like him. Now imagine another person I do not like, Mr. Donald J. Trump, in the same situation. Would he sneer at his own image or would he perhaps rather sue it? Or would he simply shoot the mirror? So, if the difference is clear, the unstranslateability I am refering to is the English sort, not the US-American one.
It is probably no coincidence that one of my heroes, Mr. Charles Darwin, himself an Englishman too, is thought to have been the first to observe the relation between sneering and snarling, stating that
The uncovering of the canine tooth is the result of a double movement. The angle or corner of the mouth is drawn a little backwards, and at the same time a muscle which runs parallel to and near the nose draws up the outer part of the upper lip, and exposes the canine on this side of the face. The contraction of this muscle makes a distinct furrow on the cheek, and produces strong wrinkles under the eye, especially at its inner corner. The action is the same as that of a snarling dog; and a dog when pretending to fight often draws up the lip on one side alone, namely that facing his antagonist.1
He claimed that sneering was a universal expression among humans, but I insist that, universal as the gesture may be, the word is protoenglish, first used as a verb in 1680 and as a noun in 1707, according to my faithful Merriam-Webster. At least that is the way I see it, because to translate it into German or Spanish you have to qualify a smile, saying, for instance: überhebliches Lächeln, herablassendes Lächeln, spöttisches Lächeln, sonrisa con aires de superioridad, sonrisa desdeñosa, sonreir con desprecio (all translations I have found in different webpages – all of them better than nothing, but are they good enough?). In German and in Spanish you have to imagine the curved upper lip, and you probably do, as the gesture is universal if Darwin was right (and of course he was). But it is not said explicitely, it is your mind that adds the detail. In British English it is explicit because of the meaning of the word itself.
Talking about the relation between sneer and snarl, It seems interesting to note that Wikipedia says that snarling is a sound, not a gesture, but illustrates it with a gesture, and that the gesture does have a German name: fletschen (but still not a Spanish equivalent). That could be a useful hint if we want to find a translation for sneering. But fletschen is used only for animals2, not for humans
Related concepts: snarl, Flehmen response3
1 Charles Darwin, The Expression of Emotions in Man and Animals, 1872, p. 251
2 Duden: [von Tieren] als Ausdruck der Aggression dem Gegner die Zähne zeigen
3 Merkwürdigerweise kenne ich flehmen von meiner verstorbenen Katze als die Geste und Geräusche, die sie machte, wenn sie Vögel durch die Fensterscheibe sah. Es hatte nichts mit Gerüchen zu tun, es war eine rein visuelle Reaktion: sie hätte sie so gerne gejagt