You don't have to sing at karaoke to have a good time, especially at this bar. This place is hopping with people who love to sing, whether they have the talent for it or they don't. Although, be forewarned that a lot of the people that sing here, really sing well. It's really fun to watch both types of groups sing. The bar is also a restaurant with really great food, so if you go early, you can grab a bite to eat or some appetizers. Karaoke is usually from 9:45pm or so till the bar closes around 1:15 to 1:30pm. There is no cover, and the DJ's really know what they are doing and how to make sure people are having a good time. Their music selection is great, and you can find anything from the old oldies to the more current top-40 songs (just ask them if you don't see it).
For an all-around good time, please visit this bar. It is T accessible (Orange Line, Malden Station), and there are plenty of Malden cabs hanging around to take you home if you drink too much.
http://www.pearlstreetrestaurant.com/