I think it's an intersection in Seattle that has one at all four corners.

There's a large section of downtown where it is basically possible to always hit an espresso stand of some sort with a well-thrown baseball, and even my humble neighborhood has a Tullys, Starbucks and SBC clustered on an intersection within baseball range, but I can't think of a Seattle intersection that has 2, 3, or 4 Starbucks in corner positions. I will investigate.

Two Starbucks do occupy diagonally opposed corners on what I take to be the busiest intersection on Robson Street in Vancouver, BC, FWIW