NPE stands for New Player Experience. Any crew has the possibility to be NPE, but some such as Nicodem and unnerfed Storm Misaki were most-certainly NPE. If an experienced player calls out NPE, I ask them how long they have been playing and if they know what a new wave release is. Not reading up on new waves or not even reading cards as an experienced player is not an NPE. It's just an idiot that loses and wants something else to blame for his loss. If I see you bring a blast master and they stack my entire crew together, am I allowed to even call it NPE when it's just an experienced player being foolish? Can I call NPE on Rasputina when I first play against her and go "nah dawg I don't need to read your cards, I'll wing it"? Experienced players are not allowed to call NPE on something as the N in NPE is missing. It's just a casual player meeting something for the first time and not paying enough respect to it.
I was pretty sure most people used NPE as "negative player experience" meaning that even if you play your best whatever makes the model have an NPE (I know way more of these from Warmachine) makes the match almost unwinnable.