When Beatrice first hears that Benedick, along with Don Pedro and the other soldiers, are coming to Messina, Beatrice immediately begins to mock Benedick. She says he's a "...valiant trencherman; he hath an excellent stomach." She is saying that he's a good eater and that he eats a lot. This is an insult because she suggests that Benedick is more interested in satisfying his desire for food rather than his desire to be a good soldier. She asks the messenger who tells Beatrice and the others that Don Pedro and his men are coming how many of the enemy has Benedick eaten. This confuses the messenger who does not know of the "merry war" between Beatrice and Benedick. That's when Beatrice calls Benedick the valiant trencherman. When Benedick arrives, he and Beatrice begin exchanging insults immediately.