''The big middle-finger moment for me was when I saw the '80s movie 'Take This Job and Shove It,''' says Adam Blank, 33, author of Field Guide to the North American Bird (Ten Speed Press, $9.95), a shockingly well executed new guide on how to flip people off. ''Robert Hays is riding in his Mercedes and he cuts off a truck and they honk at him and he gives them the Pristine'' -- i.e., the most offensive form of the finger, notable for its half-knuckle and thumb extensions. ''And I thought, 'Omigod, YOU CAN DO THAT? What is he doing with his hand?' That was the best middle finger I've seen in my life. I was 11 years old.''
Years later, Blank and his younger sister Lauren (credited as the book's coauthor though, he says, ''she didn't write anything'') started coming up with fresh and incredible ways of flipping each other off behind Mom's back. Now the Blanks have committed beauts like the Scratch, the Thinker, and the Pointer to print. The result is hilarious, and so is Adam when he shows off his moves. ''My friend Oliver's wife gave me one called the Viagra,'' says Blank, as he feigns, with an old silent-film comic's aplomb, the popping of a pill that forces his middle digit to inch slowly skyward in vulgar salute. With enough practice, he insists, anyone can become a Master Birder. ''You teach yourself,'' he says, ''because it's important!''