In another forum I read the following amazing thing:
"In the middle 1980s, when I was in the Navy, the submarine I was in operated out of Holy Loch, Scotland. Our Xerox copier needed maintenance and the American Xerox tech was on leave. So a tech came out of Glasgow. I had a junior yeoman, an Alabama Black, escort the Glaswegian. The two of them were reduced to writing notes to each other. They had no trouble reading the other's written English, but the two accents were so strong that their spoken English was mutually incomprehensible. However, if you had asked either of them, they would have told you that they were speaking their native language, English."
Have you had similar (comparably extreme) experiences? Please, only native English speakers (obviously there are many examples from or with non-native speakers)!