A trainload of subway riders was startled and a little starstruck Saturday afternoon when Assemblymember Mark Leno stepped on board at Civic Center heading toward Embarcadero. "Look who it is!" yelled a guy on a Rascal (we kid you not) and Mark was all smiles and waves. "Going to the parade," he explained, gesturing to the vaguely tranditional-Chinese-style shirt that he was wearing. "Nice outfit," said a guy with a shopping bag full of six-packs, to which Mark replied, "gotta wear the right drag."