The presence of Romeo's friends as they walk to the party juxtaposes Romeo's mood.
How does Romeo's mood contrast that of the other characters' in this scene?
Romeo is a hopeless romantic, motivated by his urge to find his true love. His friends bawdy humor indicates that they are only motivated by lust.
Romeo is still depressed over Rosaline's unrequited love. Mercutio, Benvolio, and the other partygoers are upbeat and excited about the night's festivities.
Romeo's talk with Benvolio in the previous scene has given him a brighter outlook on love. His friends however, have seen the pain caused by Romeo's failed relationship and have vowed to swear off love.
Romeo is fearful of attending the party because of the feud between the Capulets and Montagues. His friends are the opposite, ready to strike if provoked.
There isn't a difference in their moods. They are all excited about the night's festivities.