In Shakespeare's Romeo and Juliet, when does Juliet use irony?

Juliet uses verbal irony in Act III, Scene 5. In verbal irony, a speaker says one thing but really means something completely different. In Juliet's discussion with Lady Capulet about the death of Tybalt, she is vague and uses irony in her references to Romeo. At one point, she says she won't be satisfied until she sees Romeo dead:

Indeed, I never shall be satisfied
With Romeo till I behold him—dead—

Notice, however, that Shakespeare places a long dash after her pronouncement and the word dead. Obviously the dash is meant as a pause and an interruption. Juliet does not really wish to see Romeo dead but she does wish to "behold" him. She is simply adding the word to please her mother who is bent on revenge against Romeo.

Later in the scene, when Juliet is informed by Lady Capulet that her father has arranged for her to marry Count Paris, Juliet is immediately shocked, but is unable to confess to her mother that she has already married Romeo, so her words are again ironic:

I will not marry yet, and when I do I swear
It shall be Romeo, whom you know I hate,
Rather than Paris.

Again, she mixes truth with lies as she proclaims she cannot marry but if she did, it would be Romeo. Of course, she has already married Romeo and certainly does not hate him. Her words seem to walk a fine line between her real feelings and what she wants her mother to believe.