oh, so that's why they become less intelligible to their native friends!

I can confirm. While visiting Russia and having a few drinks with friends, I could understand everything perfectly even though my vocabulary was just a few words! Just kidding of course but we seemed to be understanding each other really well and later when everybody was sober, we recalled it being a good time.

The sober mind has been trained to carefully construct grammatically flawless sentences for the teacher. Hence the sober mind is hesitant, fearful and prone to second guessing itself.

The drunk mind he knows it not matter. Tempo and rhythm importanter. No stopping. Know not how conjugate don't conjugate. Not remember word loan other lingua. Say story no stopping manier words is gooder.

I found that I had to get over feeling like I was mocking a foreign accent, before I could become even passably-for-someone-bad-at-it good at an accent for the one other language I've ever tried to semi-seriously learn. In fact, leaning into "mocking" it was the fastest way to improve. I bet that it's easier to get past that perceived faux-pas when a few drinks in....

Same with music.

I'm pretty sure a drunk mind can read what you commented with ease and get the point, while a sober mind would get stuck and think "what is this" and do multiple takes before getting the point.