I think my favorite regionalism here in LA is the freeway notion. Ignoring the plethora of names every freeway has (and will vary based on the your mile marker) or the fact that some freeways that go N/S are marked as E/W and vice versa, my favorite is the reference scheme.
In the rest of the country an interstate is always I-something. Where I grew up, I was used to talking about I-4, I-95, I-75, Highway 50, State Road 441, etc.
Out here in Los Angeles - it's all "the" as in "the 5", "the 101", "the 210", "the 2", etc, etc.
Took a while to get used to, but now I can't imagine saying I-5, Highway 101, etc.