Rudeness is my Job

Costco and I go way back. Since high school I've been eating cheap hotdogs and buying my paper towels 20 rolls at a time, thanks to said retailer. My partiality to Costco is extensive and shameless, so when I consider that I lived here in Japan for several years in the 90s without Costco, I wonder how that was possible.
Now there is no need to endure separation anxiety, for Costco has wisely opened several warehouses here in Japan. Two of them are within reach from the Tokyo area. But a trip to Costco is now just that, a TRIP. No more jumping in the car to run and grab a gallon of milk or a ream of paper.
Thankfully, Aogu's brother Ken and wife Aya have a minivan, a membership to Costco and kind, patient hearts. So we have a tenative deal that we will trek to Costco with them once a month. Yesterday was our second trip since arriving here exactly one month ago. Koji and I got on the train at around 12:50 to ride to the station nearest Costco. After finally arriving at 2:20, we made a beeline for the hot dogs!
Koji hadn't forgotten his main attraction at Costco. As we were in the elevator going down to the main floor from the parking lot, I asked him what we should eat at Costco. He didn't reply; I should have known better than to try and have a conversation with him in an elevator, where he is preoccupied with "pin-pon (Japanese sound effect for pushing a button)".
But after we exited the elevator and headed for the door, without any prompting, he started shouting, "hot dog!". Once we polished off some hot dogs and clam chowder (not together!), we were off to shop. Let's just say we took our time.
Around 6, we were in the parking lot with our two carts, partially blocking the open parking spot next to the minivan as we tried to cram all our goods in the back of the vehicle (Honda Stepwagon--so versatile, how come Honda doesn't distribute these in the States?). Suddenly, someone started backing in to the open spot, quickly and a little too close to me and our purchases. I was alarmed, and I said, "What is he doing?" in a rather loud voice.
Then, a woman who was on the other side of the offending car and apparently with the man inside shouted back at me, "You're the one who's in the way!". I was shocked! The fact is, I was in the way, but I thought it would have been alright for her to ask me politely to move?!
This incident is probably not worth all the "press" I'm giving it here, but it was a big deal to me because I am used to--maybe even a little jaded to--Japanese politeness and the idea that every last man, woman and child in this country is automatically courteous in every situation. Now that I put it down in words, I see that my expectation was a bit unrealistic. Nevertheless, I think I have no choice but to try and increase awareness of my own politeness or lack thereof. Though I may sometimes be unconsciously lacking in this area, I don't want anyone, Japanese or otherwise, thinking that rudeness is my job.