The Geneva Convention lists everything that is considered to be a war crime. However, there are some items on the list that just seems to be rather strange, and you wonder why on earth it is thought to be a crime.
For example, in a war it is illegal for you to pretend that you are dead to then draw in the enemy and either kill them or capture them. It is simply regarded as being unfair because, in their eyes, it needs to be a fair fight rather than trying some sneaky methods to gain the upper hand. Of course, the reality is completely different which is why it is constantly being broken by all sides to such an extent that it is very rarely enforced.