Many societies have a saying for forgetting one's roots and pretending to be something you are not. In Chinese societies, they sometimes describe someone as a banana: yellow on the outside but white in the middle.
So what is the equivalent in Malay? It seems to be kacang lupa kulit ('a peanut that forgets its skin'). (This occurred on page 3 of the Media Permata of 10 August, in an article with the headline Jangan khianat negara, or 'Don't betray your country'.)
Slightly different is the saying buang batu ('throw stones'), though I can't quite figure out the image of throwing stones. It might be comparing the discarding of old friends as similar to tossing stones away, so perhaps it is more about forgetting your old friends than putting on airs.
And then there is the (slightly rude) Brunei equivalent jubur itam ('black backside'). The idea here is that someone pretends to be white but forgets that their backside is still black.
Anyway, I've been in this part of the world for so long that I think I'm a bit of a cheese sandwich: white on the outside but yellow in the middle.