As a performer, he is a relic of an earlier era: a Japanese Ronnie Barker or Norman Wisdom. He then surprised everyone by reinventing himself in middle age as an independent politician. Four years ago, in an astonishing upset, he was elected mayor of Osaka, a city with a population and an economy larger than many nation states.
His first term was so successful that last spring he won again, with a record majority. But Mr Yokoyama's victory, his political achievements, and even his comedy career have been eclipsed by an incident which took place in a parked election van three days before the poll.
A graphic account of what happened was given in court last month by the other occupant of the van, a 21-year-old female student who was canvassing on the comedian's behalf. After a morning's campaigning, she said, he climbed in beside her and drew a blanket over the two of them. Soon she felt a grip on her thigh, and for the next half-hour the mayor subjected her to an onslaught of determined groping.
Next day she filed a complaint, and last week the 62-year-old Mr Yokoyama broke another record when he was ordered to pay 11m yen (pounds 65,000), the largest damages ever awarded to a Japanese victim of sexual harassment.
Ten years ago, the mayor's little assault would almost certainly have gone unnoticed; indeed, until recently Japan did not even have a commonly used term for his offence. When the subject began to be aired in the early Nineties, the Japanese media invented the expression sekuhara, a merciful abbreviation of the borrowed phrase sekushuaro harasumento. These days the word is seen and heard everywhere: in the media, the courts, universities, and in the offices of increasingly nervous Japanese companies.
If official figures were anything to go by, sekuhara would not appear to be a problem at all. Japan's prefectures received just 7,019 complaints last year, an insignificant total in a population of 125 million. The previous year's count, however, was little more than one-third of that, for, like much sexual crime in Japan, harassment is grossly under-reported. What the increase suggests is not a sekuhara boom, but a growing awareness among Japanese women of where the line is to be drawn between the cheeky and the abusive.
Like many social changes, it began with pressure from outside, specifically from the US state of Illinois, where Mitsubishi Motors has a large assembly plant. In 1996, a group of American women there filed a sexual harassment suit and eventually won a $34m (pounds 21.5m) settlement. Japanese corporations then began seriously addressing the problem. In April, a revision to the Equal Opportunities Law finally outlawed sexual harassment.
As well as drawing up a code on sekuhara, companies must have a department responsible for dealing with complaints. A guidebook on preventing sekuhara has become a bestseller, with its simple explanations of sexual misbehaviour aimed at the lowest common denominator of male chauvinists. "Gazing intently at a woman's breasts or hips" and "forcing women to serve drinks or making them sing karaoke duets", it says, are "red-card offences". "Yellow-card" violations include asking female colleagues for their measurements and ostentatiously reading pornographic magazines.
The Nikkei newspaper, Japan's equivalent of the Financial Times, has put out a video with similar advice for new company sekuhara counsellors. Among its tips is to avoid responding to complaints with remarks such as: "You were harassed because you're such a sweetie."
"It's good to see it being discussed at long last," a female manager at a Tokyo trading company said last week, "but when you see how surprised and clueless these men are, it makes you realise how far there is still to go. They're genuinely amazed that women should be bothered by these kinds of things."