Accents are hard. As someone who has embarrassed himself attempting to speak at least three languages other than his native English, I can say this with conviction. And those were attempts at full conversation. Let's not mention the memorized phrases that I've managed to mangle in Polish, Chinese and Albanian.
But then I'm no actor. And I'm not called to take roles where, 1, I have to accept the role of someone from another culture and, 2, speak in that character's native accent. The list of actors who have done so well is long, though any such list would have to start with Meryl Streep. Brits such as Daniel Day Lewis and the Australian Toni Collette aren't too bad either.
But the list of those who do accents poorly is arguably even longer. As the embed below demonstrates — though, I would take issue with Brad Pitt's performance in “Snatch.” It may not have been perfect Irish Gypsy (Pikey), but it certainly fit the role.
(I would add this the list is depressingly contemporary. Go back and check out some of the performances by such classic film actors as Paul Muni, Spencer Tracy and even Michael Caine — and we'll comment about those bad trailers on some future blog post).