Stopping for lunch at a Manhattan Burger King, New York Times 'On Language' columnist William Safire ordered two 'Whoppers Junior' Monday. 'A majority of Burger King patrons operate under the fallacious assumption that the plural is 'Whopper Juniors,'' Safire told a woman standing in line behind him. 'This, of course, is a grievous grammatical blunder, akin to saying 'passerbys' or, worse yet, the dreaded 'attorney generals.'' Last week, Safire patronized a midtown Taco Bell, ordering 'two Big Beef Burritos Supreme.' 