The Xbox consoles are not popular in Japan. That doesn't mean those game machines lack hardcore fans. They certainly exist in the region. And, online in Japan, there's a disparaging nickname for them: gropers.
The Japanese word is "chikan" (痴漢), which translates as "groper" or "molester". "Chikan" is certainly not something anyone wants to be called, but online in Japan, it's how hardcore gamers mock Xbox fans. The nickname, however, is not used for those who own and enjoy other Microsoft products. Windows is used widely in Japan, and those OS users are not called "gropers".
It's also a word that you can see on Japanese public transportation, either on notices or via PA announcements that point out the obvious: "Chikan ha hanzai desu" (痴漢は犯罪です) or "Groping is a crime". Some in Japan dislike these warnings as they imply that everyone could be compelled to touch fellow passengers on the train, which is simply not true. Regardless, groping has been enough of a problem to warrant said announcements as well as women's only carriages.
Xbox fans aren't the only ones with mean nicknames. As previously posted, Sony fans in Japan are dubbed "cockroaches" online. (Nintendo fans have an unpleasant nickname of their own, and Kotaku will be covering that in the future.) It's worth noting that these nicknames are typically found on 2ch's game hardware threads, especially when things get heated. However, you can also find them in the comment sections of popular Japanese game blogs.
The groper nickname originated back when the first Xbox launched in Japan in 2002. According to Nico Nico, the media interviewed people lined up at Akihabara retailer Messe Sanoh for the Microsoft console. In a separate line, there was a customer waiting to buy an adult computer game called Ryoujoku Chikan Jigoku who also said he planned to buy the Xbox. Thus, "chikan" apparently came into use online to describe Xbox gamers. Games like Dead or Alive, Dream Club, or Japan-only visual novels with young female characters only reinforced the "chikan" nickname and made the Xbox seem like a pervy console.
(In 2008, there was an incident in which a PSP owner was accused of using the Sony gaming handheld to illicitly photograph a woman on the train. The "chikan" term was, for a brief while, thrown back in the face of Sony fans.)
The nickname was even modified by some during the Xbox 360 years to be a slur against Koreans. Xbox fans were still dubbed "chikan", but with one of the kanji characters switched out: "Chikan" (痴漢), which means "groper", became "chikan" (痴韓), which literally means "foolish Korea". Here, the character "kan" (韓) refers to South Korea, which can be called "Kankoku" (韓国) in Japanese. All Japanese people did not use this slur! However, it did exist, and thus, I am pointing it out. Japan has a significant number of Korean-Japanese as well as people who enjoy South Korea, its food, its culture, and its people. However, the internet, wherever it is, succeeds in bringing out discrimination. The reason why this spin on the word came into use was because at that time a Korean American was an exec at Microsoft Game Studios, Xbox 360 demo kiosks in Japan used Samsung televisions, the Xbox 360 had Samsung parts, and because there was an Xbox 360 update that gave South Korea ownership of a disputed island. Also, everywhere there is internet anonymity, there are people discriminating -- that goes for the West, too!
As opposed to "chikan", the less offensive and unsettling way to refer to Xbox fans in Japan is simply "MS shinsha" (MS信者) or "Xbox shinsha" (Xbox信者), with "shinsha" (信者) meaning "believer" or "follower". Basically, you're calling someone a zealot.
While online "chikan" is still the standby to mock Xbox fans, Microsoft's upcoming console, the Xbox One, already has a new nickname in Japan. While it's called "Xbone" in the West, it's being called "divorced" in Japan. In comparison, that's not so bad.