Let’s Settle This Once And For All: Is Idaho Considered PNW?

Admittedly geography has never been my strong suit. I think I can still name all the state capitals but that's only because of the classic Animaniacs song:

Baton Rouge, Louisiana; Indianapolis, Indiana
And Columbus is the capital of Ohio
There's Montgomery, Alabama, south of Helena, Montana
Then there's Denver, Colorado, under Boise, Idaho.

I love that Boise is in the first verse of the song. But when it comes to what the various regions of the country are considered, I'm a bit lost.

I grew up in Nevada, which is just a desert and that's easy and makes sense. Elsewhere things get weird. According to the U.S. federal government, the south includes Delaware, D.C., Maryland, Virginia, West Virginia. I've never heard any of those be called the south. And I think we can all agree that Florida is its own thing entirely.

When it comes to the Pacific North West it appears that Idaho is technically included along with Oregon and Washington. So why do my friends living in Oregon and Washington reject Idaho as part of the trio? A listener who called into Moug & Angie Mornings who is from Washington even joked about no longer living in the PNW but I totally thought she did. Am I naive in thinking I can claim PNW?

Some contend that Idaho is technically a Rocky Mountain State instead, but why can't it be both? Is there a cultural component of which I'm not aware but should be? I remember a Sicilian friend in high school being offended at being called Italian because of some very specific cultural aspects. Is this similar? Settle this for me and please explain!

(WorldAtlas/CityData)