War Crimes fall in to two distinct categories. One is naughty and the other is very naughty indeed.
Naughty War Crimes
A naughty war crime might (for example) be something as straightforward as getting together with a few mates [Ideally around a dozen or so... or was that Kelly's Heroes?] and trying to rip off a bank or stage a bullion heist whilst everyone else is concentrating on killing each other. It's a crime, and it's war, so it's technically a 'war crime'. Believe it or not, this has happened more than you'd think. After all, with all the confusion of conflict, it's the ideal opportunity - and you're already tooled up. Bargain!
Very Naughty War Crimes
A very naughty war crime might (for example) be 'merely following orders' - that is being complicit in the systematic slaughter of millions. Another very naughty war crime might be illegally taking a country to war based on a strategy worked out at lunchtime on a beermat... or no strategy whatsoever... just a pile of bollocks... for instance. But nobody in their right mind would be that fcuking stupid... would they?