Though they’re operating on only half a name, the Grandsons still give twice the entertainment value of the next leading band. Quirky, catchy, inspired, and sometimes goofy, the pioneering group continues to defy categorization. Let’s just file them under “Fun.” At 9 p.m. at the Cowboy Cafe South, 2421 Columbia Pike, Arlington. FREE. (703) 483-3467. (DN)