When people refer to parts of the area by nicknames, and act surprised that you don't know where it is. A long time ago, my mom was showing some visitors around our hometown. As she was planning the itinerary for the next day, she said something about changing how we were going to get to Hughes Stadium "so they won't have to see Millertown". I had no idea what she was talking about, and asked her. She told me if I didn't already know, then I didn't need to know.
Finally came out that Millertown was the derogatory name she used for the poorer section of our hometown. I'd never heard it before and never heard it since (maybe it's a real thing, maybe not), but I remember how annoyed and irritated I was that she expected me to know this without ever having to tell me!
More recently, a coworker told me that I would love a store over by where she lived, and I should really go check it out sometime. I asked where it was, and was told "Okay, you know where Spaghetti Junction is? It's just north of that, off the *whatever* exit". Yeah. I may have lived here for 10 years, but I still don't know what that is, and the total look of shock I'm getting when I ask you where Spaghetti Junction is reminds me of why I don't ask these questions! It took me 6 years to figure out what the Crosstown was, because nobody would connect the actual name of the highway and it's nickname together for me to figure out. AGH!