[MMM]

Let's keep in mind that the Karaoke bars (at least the ones in America) don't really exist in Japan. In Japan you go to Karaoke Boxes which are private rooms you share with friends and order tons of food and drinks. But you aren't singing in front of strangers.

The only place I know to sing with strangers would be a snack bar. These tend to be extremely expensive by tourist standards. (Dropping a couple hundred dollars is very common) so you wouldn't only want to go with a trusted friend (especially if he's paying!)