the "r" sound in wash is a legit western accent that goes way back. This is like complaining about the dropped "r" in a Boston accent.

I know no native Warshingtonian (sic), even those whose families go back several generations, who add an extraneous R. Everyone I know who pronounces it that way hails from the midwest. Thus do I reject it.

That is odd. My mother from Tacoma and her mother from Idaho as well as my mother-in-law from Idaho all say wash with an "r" sound. therefor "Washington" also gets the "r" both mothers are 4th generation NW native with ancestors who migrated here on the Oregon trail.

It is true that those who are younger than 60 have dropped it, but that doesn't make it incorrect or Midwestern. Just old fashioned.

Well, I don't add it (I'm a native), and my stepsons are actually 5th-generation (honest!) - and none of their uncles, their mother, or their grandparents ever added the R. I do remember a large number of people who used to pronounce it that way, but all the ones I knew were midwestern transplants. Most of them said "Boeings" too.

Not accepting it would lead to you being annoyed, either silently or vocally correcting the person.

Speaking of the Ave, I don't mind "The Ave" at all, but I do get annoyed when bus drivers (or anyone, really) use the phrase "University Ave". It makes me cringe until I can find a new annoyance to focus on.

..is kind of a mouthful?!?!?

THAT'S WHAT SHE SAID!!!