At 5:30pm, we purchased octopus balls (not the balls of the octopus as I originally thought, but rather dough balls stuffed with octopus tentacle) and iced cocoa, and sat down to eat them.
Tom: [after seeing me pay for the cocoa] Niniane, never say "arigato" again. That's extremely rude.
Me: What? Isn't that the proper way to say "thank you"?
Tom: No, that's "arigato gozaimasu". "Arigato" is only used by a superior to a subordinate, or when you know someone extremely well. It's very rude to use it for strangers.
Me: [very sadly] Tom ... I've already used it 500 times this past week.
Tom: Well, service people won't show any unhappiness over it. Even if you cursed them as dogs, they wouldn't say anything back, because they treat the customer as God in Japan.
Me: But did I inadvertently hurt them in their hearts?
Tom: Most likely. They probably went home and cursed you.