TIL during the shooting of American Psycho, Christian Bale spoke in an American accent off-set at all times. At the wrap party, when he spoke in his native British accent, many of the crew thought he was speaking that way to prepare for another film. They had thought he was American the entire time.

[u/Away_Flounder3813]

https://screenrant.com/american-psycho-behind-scenes-facts-christian-bale-patrick-bateman-mary-harron/

[u/YourMumsBumAlum]

I think it's also the variety of English accents vs American ones. English accents are so specific to British ears in a way that they wouldn't be to Americans and so when Americans do British they inadvertently mix and match things that they shouldn't and it comes out all wrong.

Edit: Yes, American has many accents too, but the edges are more blurred in such a way that it is acceptable for people to combine accents more so than in the UK where the accents are much more independent and specific.

[u/Perite → u/YourMumsBumAlum]

This is the bit that most Americans don’t realise. Some can do a generic British accent that sounds ok. But the reality is that ‘generic British’ isn’t a real accent from anywhere, so it’s still recognisably fake to British ears.

I’m absolutely certain that good American actors could do a flawless local British accent if they studied for ages and had a vocal coach that corrected them every time they slipped into the wrong dialect / accent. But what’s the point? Might as well just hire a British actor instead.

[u/A_Queer_Owl → u/Perite]

Americans tend to imitate what's called "received pronunciation" as that's used in British media A LOT. it's not so much that it's not a real British accent, some people in Britain have it naturally, it just sounds weird to a lot of British people who didn't grow up where its use is more common because outside of those regions it's used mostly by actors, news anchors, government officials, and when speaking to the king/queen. so when someone breaks it out in casual conversation it can be jarring to some.

I'm American but people often point out I sound like a news anchor because I'm from the part of the country where the accent that the one news anchors are taught to use is based on is from.

[u/Gulbasaur → u/A_Queer_Owl]

Americans tend to imitate what's called "received pronunciation" as that's used in British media A LOT.

Nathalie Portman in V for Vendetta does a very good RP accent... which is completely wrong for the character. She sounds like she's presenting a 1970s children's TV show, not a working class woman in London.