Carl Luce meets Holden in the Wicker Bar in Chapter 19. Luce is a recognizable common type--the pseudo-intellectual middle-class bohemian. He orders a martini and specifies that it must be extra dry. He pretends to have refined tastes but is obviously shallow. When he orders his next martini he tells the bartender to make it even more dry (i.e. very light on the dry vermouth). That used to be a sign of discriminating taste many years ago. He is probably getting cheap domestic gin in his martinis but couldn't tell the difference between that and imported British gin. He is merely aping all the other pseudo-sophisticates who specify "extra-dry." His conversation is empty in spite of the fact that he considers himself and represents himself as a high-grade intellectual. He was Holden's senior advisor at one of the many schools Holden attended, but all he ever talked about was deviant sexual matters. Luce feels uncomfortable talking to Holden because Holden is not one of the multitude of pseudo-intellectual types who get together and gossip about each other and pretend to be ultra-sophisticated and well-informed about what passes for the latest in "culture" in the big city, usually something avant-garde and worthless. Luce and Holden are incompatible because Luce is obviously an extravert while Holden is a fairly extreme introvert.
It is significant that Luce keeps asking Holden to "grow up." That is definitely Holden's problem; he is suffering from growing pains. But Luce is only a few years older, an undergraduate at Colombia, and not yet very grown up himself, just trying to act the way he would like to be. Luce is a complete phony, probably the phoniest character in the entire novel. He is really so common and ordinary that everybody has known Carl Luces and recognizes the type immediately.