that's so east coast

Usually used when referring to something that is somehow affiliated to the east coast. This phrase is also used when referring to a person's actions, an article of clothing, an object, et cetera, and how they relate to east coast stereotypes.

When using the phrase, that's so east coast, usually, you would hear it come from "east coasters" (people who were born on the east coast) or from people who were born on the west coast who think they are as cool and preppy as the east coasters.

C: You know what I've been loving recently?
A: What?
C: Pizza! Especially New York style.

A: Oh my God. that's so east coast!

C: I know, right?