Most Japanese people cannot refuse to sing a song. People who do not have a large song repertoire get into a trouble. They have a hard time not corrupting the party's festive atmosphere. However, there hardly is a case when any one of the group member does not sing, because everybody is forced to sing. Only one song is enough.
Karaoke boxes are small rooms with karaoke machines.
A group of people go there and spend an hour or two. The people in the box try to sing as many songs as possible to save money. While one person is singing, other people are looking rigorously through the karaoke piece list, wondering which piece they are going to sing next. People usually do not listen to the other person's singing seriously unless the singer is very skillful. It is the same way in the karaoke bars.