Oh-so-young and oh-so-British, Supergrass nonetheless lacks the grandiosity of much of Britpop’s latest assault force. Rather than vow to live forever, Supergrass songs live from minute to minute, creating compelling vignettes out of such passing rebellions as the decision not to sit up straight on the bus. With Triple Fast Action at 8:45 p.m. at the 9:30 Club, 930 F St. NW. $8. (202) 393-0930. (MJ)