My favourite approach is to create situations that evoke a common reaction in the reader and then have the character react in a non-obvious way. The contrast between the natural reaction and the 'unnatural' one should be enough to create a sharp contrast.
The yelp had his head turn around automatically. A toddler had fallen and was whimpering as the mother squatted beside him, whispering some smiling comfort. Good thing he was too far to listen to any 'oh, mamma will kiss the boo-boo and the pain will go right away'. It was enough he could still hear the whining.
It's important that the description of the scene is impartial - no hint of subjectivity. The reader must know how a normal person would react from the situation, not through words. To have the narrator use adjectives, for example, pointing to warm, fuzzy feelings and then contrasting with the cold, harsh feelings of the character would feel like the narrator is obviously manipulating the reader.
In the example I give,
whispering some smiling comfort
we are facing a factual description, despite all. The mother is whispering and she is smiling in a way that is meant to be comforting to the child. Notice that the reference to 'some' can (we'd need tone for that) be interpreted in a dismissing way. Once the narrator presents the character's reaction, 'some, can be seen in that light, but until then it can also have a neutral conotation.
What wouldn't work as well would be something in the lines of...
A toddler had fallen and the poor little boy was whimpering as the mother squatted beside him, whispering some loving comfort.
The idea of the child being a 'poor little' child would be too far removed from the character and identifying an action as 'loving' would likely be too far from him too. That sweet idea of 'loving' would have to be balanced with a dismissive reference to it.