One song which is often quoted or alluded to when discussing pronunciation differences (and even differences of any kind) is “Let’s call the whole thing off“, by George and Ira Gershwin, first sung by Fred Astaire and Ginger Rogers in the movie Shall we dance?. The relevant part starts:
You say either and I say either,
You say neither and I say neither
Most versions of the lyrics online don’t help by not indicating the pronunciation (apparently, neither did the sheet music; Wikipedia reports that Ira Gershwin told the story of one singer who sang the song with the same pronunciations throughout), so I will write:
You say ee-ther and I say eye-ther,
You say nee-ther and I say nye-ther
This also doesn’t help by not indicating who is singing, therefore making it clear who says this and who says that. In the movie, he sings this part, so I will write:
|she says||he says|
The whole song can be summarised as:
|She says, likes, wears …||He says, likes, wears …|
All but the first two and last illustrate the three most common pronunciations of <a>, /æ/ as in trap (sometimes called ‘short’ or ‘flat’ a, /a/ as in palm (sometimes called ‘long’ or ‘broad’ a) and /eɪ/ as in face (a diphthong). Pajamas, laughter, after, Havana and banana can all be pronounced with /æ/ or /a/. For these words, the /a/ pronunciation is more common in Southern England, Australia, New Zealand, South Africa and parts of the New England and Southern regions of the USA, and the /æ/ pronunciation in the other parts of the UK, Ireland and the other parts of North America.
Tomato can be pronounced with /a/ or /eɪ/, with Southern English etc speakers using the former and most US and Canadian speakers using the latter. As far as I know, potato is always pronounced as po-tay-to, and po-tah-to is just a silly joke by Ira Gershwin for the sake of a rhyme.
eye-ther and nye-ther are associated with Southern English etc speakers and ee-ther and nee-ther with North American speakers. Dictionary.com reports that both pronunciations have been used in British English, but eye-ther came to predominate in the 19th century. It doesn’t explain why, or why ee-ther came to predominate in North America.
As far as I ever knew, everyone says oysters, but while researching for this post, I found that the pronunciation and spelling ersters is associated with New York City and Louisiana, which shows how the same pronunciation can occur in widely separated areas. Maybe there is an explanation for that.
There’s a problem with the way Astaire and Rogers sing the song, and that’s that their pronunciation switches halfway. If she wears pa-jam-mas, we would expect her to say laff-ter, aff-ter etc. I suspect that Ira Gershwin wrote the words for one person to sing, and the director divided it without consulting him or a linguist. If we swap their pronunciations of laughter, after, Havana and banana, we can say that Rogers’s pronunciation is typically American, while Astaire’s is closer to what is usually called Mid-Atlantic, a blend of American and British pronunciations used by American performers in the early to mid-20th century.
The issue arises, and they sing the song (and dance on roller skates) immediately after the following dialogue:
She: I don’t know what to do.
He: I don’t eye-ther.
She: The word is ee-ther.
He: Alright, the word is ee-ther. No use squabbling. That will get nye-ther of us any place.
She: The word is nee-ther.
This dialogue is obviously contrived to lead into the song. I’m not going to watch the whole movie to check their pronunciation throughout, or whether she corrects him on any of them (or even notices).
I don’t know how much of the pronunciation in the dialogue and song are Astaire’s and Rogers’s own pronunciation, and how much they are modifying their speech for the movie. According to Wikipedia, Astaire’s character is an American who has been performing in Paris. From their movies which I have seen, they seem to play the same kinds of characters in the same kinds of ways in each. Astaire seems to be more comfortable with the alternative pronunciations than Rogers, unless she is deliberately exaggerating and mocking his speech.
There are various performances and versions of the lyrics online. In some cases the pronunciations are not the performer’s own. Whichever of Ella Fitzgerald and Louis Armstrong sang the ‘English’ pronunciations in their version, didn’t speak like that in real life.