Neutral Evil Alignment

A Neutral Evil character is only out for themselves. Nothing else matters to them. Whatever they want – power, wealth, reputation – they won’t follow someone else’s codes to get it. They will do whatever they must. If they want something, they will take it. If that means betraying a friend, they will do it. The motto is to keep what is useful and to discard what is not, regardless of what it is.
They don’t believe that following laws and traditions makes anyone a better person. Law and order props up and protects the weak and holds the strongest back. But law and order does have its use as a tool to manipulate people who believe in honor, loyalty and promises. Neutral Evil characters make allegiances with others to further their own agenda but will quickly hurt, desert or betray allies when they are no longer useful. In the same way, they will play along with laws if they happen to align with their ambitions, but they will not hesitate to break them if they don’t.
Neutral Evil characters are smart, though. They won’t go around breaking every law especially if they will be caught. Instead, they will weigh up their options and decide if risking the consequences for breaking a law is worth it to get what they want. They will also weigh the immediate potential benefits of betrayal against the long term benefits of staying loyal. They are not wasteful especially not of their social currency since they spend a great deal of effort into that.

Characters with a Neutral Evil alignment will harm others if it furthers their agenda. They don't kill for pleasure. They use violence like everything else: as a means to an end. If the violence doesn't serve a purpose then they don't bother with it. No effort is wasted.
Because a Neutral Evil character has no organized codes to follow and they are Evil they will harm innocents, hit weaker and unarmed foes and see nothing wrong with using poison. They will fight dirty and use nasty tricks. Whatever it takes to win.
A Neutral Evil character is an unpredictable and dangerous ally to have. The kind of person who will betray their own family and hurt others for personal gain is not someone that can really be trusted. You never know at what point you will stop being useful to them – and you don’t want to find out what will happen to you when that day comes!
Given their love of power and money, if someone offers them enough they will switch allegiances without a second thought. All they want is to come out on top. They will take the easy road to get there and stuff everyone else.
From a Neutral Evil character’s perspective, they are better than everyone else because they only have to care about making their life the best without caring about anyone else. They waste nothing. For everyone else, a Neutral Evil character is terrifying because they can be driven by purely selfish desires without any honor to hold them back.