Mercutio changes his tone from one of annoyance and concern to one of bawdy humor. At the beginning of the scene, Mercutio is worried about Romeo because of the time he wastes pining for Rosaline and because of the "challenge" that Tybalt has just sent to Romeo. Mercutio shows his true worry through annoyance with Romeo before he appears. He asks things like "Where the devil should this Romeo be?" (2.4.1) and refers to Rosaline as a "pale hard-hearted wench" (2.4.4). As soon as Mercutio begins talking about Tybalt, Mercutio's tone changes. Tybalt remains on the side low-class humor for the rest of the scene. Tybalt is described as fighting "as you sing pricksong" even though Mercutio demonstrates Tybalt as a very able duelist. When Romeo enters, Mercutio compares him to a fish and begs Romeo to return Mercutio's puns with ample wit. Romeo does, and Mercutio is delighted. Mercutio, then, is encouraged to get even more crass as the scene goes on, even to the point where he insults Juliet's nurse: "[The fan] to hide her face; for her fan's the fairer of the two" (2.4.105). Romeo has to wait for Mercutio to leave in order to speak seriously to Juliet's most trusted caregiver. Most interesting, though, is Mercutio's own reason for his mood change:
Why, is not this better now than groaning for / love? Now art thou sociable, now art thou Romeo; now / art thou what thou art, by art as well as nature. (2.4.87-89)
Therefore, as always, Mercutio proves that he is a fabulous friend (or even morethan a friend). Certainly this is a fitting precursor to Mercutio's pending death for Romeo's sake.