Back when I was studying stage speech at Pittsburgh Playhouse Theatre School, a good friend of mine came to visit me in Pittsburgh.
When my friend heard I was taking the course, he asked me to take him to attend a class. This was natural: My friend was the one who worked on my accent before. He is a linguist, and often helps people with their English.
I took my friend in and asked the teacher if it was OK. As soon as he agreed, my friend said: "You're from New Jersey!"
The teacher was very surprised, and asked my friend how he knew.
"From your accent," said my friend.
"I don't have an accent!" said the teacher. But my friend insisted that the Jersey accent was quite discernable. Remember, my friend was an expert on accents, but my teacher was still not too happy about it.
Years later I mentioned the story to the director of Nicolet Theatre. He said that is the most embarrassing thing that can ever happen to a speech teacher.