To answer this question, one should keep in mind that education of a country regime plays an important factor on issue like this one, of the question.
The short answer is, Cambodians considers Vietnamese as “enemy of generations”, it isn’t a hatred which they would like to call for an end, the reason why we SHOULD generalizes Cambodian, because generality works, it is simply blinding yourself for if you chants the fashion mantra ““not all of them”, there must be an accurate generality to applies a group of people, the matter is, whether it is a correct one or a wrong one, initially a group of people needs to be defined by some properties, some are essential properties which qualifies the group of people as who they really are, and some are accidental properties, accidental property is the generality that we are talking about in here.
Back to the question here, the reason why Cambodian hates Vietnamese, because the Cambodian regime is too backward that, it is extremely poor and lacking resources on it’s own, and I am even talking about intellectual resource, it is very easy to brainwash people who has no productive life in their own society, especially lacking materials likes, smart phone, desktop computer and so on. For a regime which is fear of letting it’s citizen to find out both of it’s internal corruption and it’s political weakness, the easiest weapon is propaganda of hatred toward aliens, since it is a historic fact that there were a lots of conflict between Vietnam and Cambodia, Cambodian government must utilizes it to provokes it’s citizen to switch their attention of stressing toward outsider, hatred toward vietnamnese is just one of the many, and according to the Cambodian government, it is better for it’s citizen to have it than do not have it, so that they can convinces people to blames problem toward outsider. As a result, Vietnamese people is being hated by Cambodian in general, it doesn’t mean majority of Cambodian hates Vietnamese, although it could be, but it means that, it is SO EASY to come across a Cambodian who hates Vietnamese.
In a society where free speech and free press are neither encouraged nor being protected, people’s way of thinking can be easily manipulated, especially for the conceptions that I brought up on this post, such as, essential properties of a group, accidental properties of a group, and how generality works etc. people in closed society can’t easily to grasp these conceptions, what to speaks of the case in Cambodia? This also remind me how open Vietnam is, as compare to first world countries like japan, japan which’s still a close society by norms, it’s easy to come across an individual who is too backward that, he or she is unable to catches a bit of common sense from a open society, this doesn’t happen in Vietnamese society, regardless the socialist republic of Vietnam or viet kiu communities in oversea.