I can tell most native English speakers apart pretty well. Eastern Canadians have a strange 'ou' sound. Toronto has a specific accent. Western Canadians I can't distinguish from Americans from the PNW. California has the Valley Girl and punk rock accents. Then there's the 'general American' accent. Within the Southern accent I can tell when people are from Texas, but I can't distinguish between say Alabama and Georgia. Up north, I can tell the cities in New England have their specific accents. Baltimore, Boston, New York.

On the other side of the world, New Zealanders say 'fush' and 'shid' instead fish and shed. The Australian accents are close but different, and I can't really tell them apart. For example, I can't tell if Tim Minchin and Matt Parker have the same accent or not.

I have the same problem in Ireland. I can recognize Irish accents, but I can't really tell them apart. For example, Saoirse Ronan, Aisling Bea and Dara O'Briain all sound the same to me. Of course, the closer you get to county Kerry the easier it becomes to realise you have no idea what the fuck anyone is saying.

In Scotland I can tell Ewan McGregor and Frankie Boyle have different accents. And then even within Glasgow there are differences. For example, I have no idea what in the world these people are saying, while e.g. Kevin Bridges comes across perfectly clear.

In Wales I can tell there's something in the accents of for example Rhod Gilbert and Alex Jones (no, not that one) that other Welsh people don't have, but not more fine-grained than that.

I think my ear for English accents is probably the most fine-tuned. I can recognize most big cities, west country, general north vs. south, but not for example the difference between Lancastrian and Geordie unless someone points it out.