The Scarlet Tree 6521 Roosevelt Ave NE, 523-7153. I was ready to settle in with a few dozen bourbons-on-the-rocks and indulge in my favorite Tuesday-night activity--bitching about the world--at the Scarlet Tree, which is no dive, but no pretentious hipster joint, either. But then Brian showed up. Brian is the karaoke master, and what a setup he's got: spinning colored lights, wireless mikes, and something like 12,000 songs. It wasn't a huge crowd, but it was pleasantly mixed: older, younger, and a couple of kind regulars who compliment you, no matter how bad you sing, there under a sea of tiny disco balls. EMILY HALL