noun
riding double; two people on one bike/motorcycle
Slang term for two people riding on a single bicycle or motorcycle, often illegally. Common in youth and biker subculture.
ニケツは危ないからやめとけ。
Riding double is dangerous, so don't do it.
あのカップル、よくニケツしてるよね。
That couple often rides double, huh.
noun
sharing a seat; sitting two to a chair
Extended slang use for two people sharing one seat or chair, often in casual or cramped settings.
椅子が足りなくて、ニケツで座った。
There weren't enough chairs, so we sat two to a seat.
Standard term for riding double; ニケツ is slangier and more casual.
Abbreviation of 二 (ni, 'two') + ケツ (ketsu, slang for 'buttocks'), literally 'two butts', referring to two people sharing a seat or vehicle.