Kevin Costner in Robin Hood. Perhaps the worst casting decision ever. It sounds like a North Dakota cowboy time traveled to 12th century England.
The English regional accents became a bit confusing at times as well, varying from Lancashire to Welsh often from the same actor.
That happens a lot, Gimli's accent in LOTR as an example, he jumps from Welsh to Scottish. The only time imo that it was successful was in Braveheart where the Irish actors were playing Scots and "Irish Stephen" was played by Scots actor David O'Hara. Most native Scots can move seemlessly into an Irish accent and vice versa however there's always the exception - Gerald Butler ;D
It seems to be in vogue just now for fantasy or fairy tale characters to have a Scottish accent - cue.. Shir Shean Connery! who never gives a damn what accent is asked of him.
Playing an "Irish" cop
I don't even recognise what kind of Scottish accent he has!!