Shakespeare's works are rife with sexual innuendo. Remember that the plays were performed to live audiences and these jokes and puns were used to further entertain the crowd.
Some examples from Romeo and Juliet include:
Act 2, Scene 5, Nurse to Romeo:
Hie you to church. I must another way,
To fetch a ladder, by the which your love
Must climb a bird's nest soon when it is dark.
I am the drudge and toil in your delight,
But you shall bear the burden soon at night.
Here the Nurse is helping Romeo get to Juliet to consummate their wedding. The 'bird's nest' and Romeo's 'burden' are both descriptions of Juliet during intercourse.
Act 1, Scene 1, Sampson to Gregory:
Ay, the heads of the maids, or their maidenheads.
Take it in what sense thou wilt.
In this scene, Sampson crudely equates sword fighting with rape. Here 'maidenhead' equates to virginity.
There are other more general puns and double meanings.
For example, any reference to a weapon/sword/knife could be a reference to male genitalia. Furthermore, "to die" was understood, in Elizabethan times, to mean an orgasm. "To stand" could also be interpreted as an illusion to erection.
The opening scene, from which the maidenhead quote above is extracted, is basically one long collection of innuendo. There are 'naked weapons,' 'thrusting,' and 'cutting of maiden heads'.
Mercutio's character is often guilty of double-speak. His 'boy talk' with Romeo describing both Rosaline, Juliet, and love in general is often marked by crude humor.