You will find what you are looking for in the character of Mercutio.
In Act I, scene 4 we meet Mercutio and quickly discover that he is the clown of the group. He is not a Capulet or a Montegue but related to the Prince.
He seems to be Romeo's best friend and in I. 4, he trys to lighten the mood. Romeo is still being self indulgent concerning his unrequited love for Rosalind. The Queen Mab speech is full of sexual jokes and innuendos. By the end of the scene, Romeo seems to be in a better humor.
The revenge motive can be found in Act III, scene 1. The fight between Mercutio and Tybalt seems to be more in jest than "out to kill", yet Romeo, stepping between the two, inadvertently causes Mercutio's death. When Tybalt returns, Romeo wants to avenge his friend's death and thus he kills Tybalt.
These are perhaps the best examples.