[titanomachy]

I’ve been addicted to video games without being physically dependent on them. I’ve been physically dependent on amphetamines without being addicted to them.

The relevant distinction isn’t what happens in your brain (which is not a useful diagnostic criterion), but whether you pursue the behavior to a harmful extent.

[chmod600]

Is that distinction really useful though? Doesn't that rope in pretty much any behavior that deviates from your idealistic expectations of yourself?

Is a nail-biter an addict?

[CobrastanJorji]

"Not your ideal expectation of yourself" is probably not enough, but if it's causing the nail-biter significant harm, then potentially, yes. If you've got someone who's tried unsuccessfully to stop biting their nails, they do it as a stress relief mechanism, it's causing significant bleeding/infection, they're hiding their hands out of embarrassment, they're having problems at work because it's grossing people out, etc, that could probably qualify as a behavioral addiction.