In years 24 and 25, when he pictured President Clinton as a floating buttered waffle and House Speaker Newt Gingrich as a lit bomb, Garry Trudeau (a.k.a. Mr. Jane Pauley) earned for the umpteenth time his eminence as a master sociopolitical satirist. But regarding the annotations in the coffee-table career surf Flashbacks: Twenty-five Years of Doonesbury, whoa, Trudeau! What possessed you to gild a dossier of comic-strip bull’s-eyes — scored in most of the 800 Doonesburys selected here from 9,000 or so done to date — with so many self-congratulatory historical sidebars? And wherefore the bilious opening homily about the mean, ”scorched-earth” quality of all other post-Watergate political humor? Trudeau dismisses even early, vintage Saturday Night Live as ”adolescent” and ”banal.” As if the 25th Uncle Duke story line wasn’t? ”The humorist without humility,” the cartoonist rightly lectures us, ”misses the fattest target of them all — himself.” Q.E.D., GBT.