SEOUL — Japan's conveyor belt sushi restaurants are struggling to regain the trust of diners, after the industry took a licking from one customer, whose viral videos of him defiling utensils and sushi with his saliva have earned him descriptions ranging from "nuisance" to "sushi terrorist."

The Japanese public's reaction suggests it's a brazen assault on two things of which Japanese are very proud, their sushi and their manners.

With a furtive glance and an impish grin, the young man in the video licks the rim of a teacup before returning it to a stack in front of his seat, where unsuspecting customers may pick it up. He also licks soy sauce bottles and smears his just-licked fingers on pieces of sushi making their rounds of the conveyor belt.

Conveyor-belt sushi restaurants have been around (and around) in Japan since the late 1950s, and have since spread worldwide. They're a cheaper, more anonymous alternative to ordering directly from a sushi chef, who makes the food to order, while standing behind a counter.

At conveyor-belt sushi restaurants, plates of sushi rotate past diners who can choose what they like. Many sushi emporia also feature tablets or touchscreens, where customers can place an order, which travels on an express train-like conveyor and stops right in front of them. Plates, chopsticks, bottles of soy sauce, boxes of pickled ginger and green tea sit on or in front of the counter for diners to grab.

Reports of various abuses at other conveyor belt sushi restaurants have surfaced, including pranksters filching sushi from other diners' orders, or dosing other customers' food with the spicy green condiment wasabi.

In an effort to repair the damage, the Akindo Sushiro company which runs the restaurant where the video was filmed, says it has replaced its soy sauce bottles, cleaned its cups, and centralized utensils and tableware at a single point. All the chain's restaurants will provide disinfected tableware to diners who request them.

The chain also says it filed a complaint for damages with police on Tuesday and received a direct apology from the man who made the video, although his motives remain unclear.

Some pundits are blaming the restaurants for trying to save money on labor costs. Fewer restaurant staff means "fraud will be more likely to occur," sushi critic Nobuo Yonekawa argues in an ITMedia report. "It can be said," he concludes, "that the industry itself has created such an environment."

Takehiro Masutomo contributed to this report in Tokyo.