Mr Fujiya said he has seen two people finish a whole bottle of soy sauce with their sushi, and others adding a large amount of wasabi.
"As a sushi chef, I feel insulted, because when I prepare my sushi, I do it already with the taste in mind," he said.
"You don't dip the rice because it will soak too much soy sauce, but just the fish side if you really have to."
He said sushi restaurants serve pickled ginger as a palate cleanser, not a topping, and it is not to be eaten with the sushi.
Mr Fujiya said other common "mistakes" include the "rude act" of the rubbing of wooden chopsticks after breaking them apart because it implies that the restaurant has poor quality chopsticks that came with splinters.
Sushi is best eaten fresh when the rice is still warm and should not be ordered as a takeaway.
"Most definitely, sushi is not takeaway food because the quality drops after just a few minutes," Mr Fujiya said.
"But here in New Zealand, more buy sushi as takeaway than actually eating at the restaurant."
AUT University professor of diversity Edwina Pio said it was incumbent on ethnic chefs to advise and educate their diners with sensitive courtesy.
"A hint with a fact sheet placed within the menu would give the intelligent diner the option to eat a samosa or roti with a fork and knife or more delicately and appropriately with their fingers; or glean information on what is a palate cleanser such as pickled ginger with sushi," she said.
"The dignity of difference can unfold wonderful initiatives through cuisine, while also providing interesting conversation anchors."
Japan Society adviser Masa Sekikawa said Japan Day, a free annual festival taking place at The Cloud on Queen's Wharf tomorrow, would provide a window into Japanese traditions and culture.
Now in its 15th year, the event includes Japanese cultural interactive demonstrations such as ikebana flower arrangement and kimono wearing, performances, food - yes, including sushi, plus yakisoba and okonomiyaki, and market stalls.
Other highlights include a live tuna filleting show, ice sculpting and the Asahi Beer Garden.
How to eat sushi
• Don't dip the sushi into soy sauce. The chef will have already prepared the sushi to taste.
• Eat nigiri sushi (rice with a topping ) with your fingers, but use chopsticks for sashimi (raw fish).
• Don't dip nigiri sushi in soy sauce. Just dip the fish side (topping) in a little sauce.
• Don't eat sushi with the pickled ginger; it's a palate cleanser, not a topping.
• Sushi is not takeaway food, it's best eaten when first made (the rice should still be warm).
• Don't add too much soy sauce or wasabi, it's insulting to the chef and overpowers the taste.
• Never rub the wooden chopsticks together after breaking them apart, it is rude.
