True, I talk of dreams,
Which are the children of an idle brain,
Begot of nothing but vain fantasy. (I.iv.)

Mercutio’s “Queen Mab” speech introduces us to an important aspect of his character. He is a cynical realist who finds dreams and fantasies ridiculous. Throughout the play Mercutio makes fun of Romeo’s fantasy of perfect romantic love, which invites the audience to question the seriousness and maturity of Romeo’s feelings for Juliet.

Appear thou in likeness of a sigh,
Speak but one rhyme and I am satisfied,
Cry but “Ay me,” pronounce but “love” and “dove.” (II.i.)

Mercutio makes fun of Romeo for using language drawn from the love poetry that was popular in Shakespeare’s day. He draws attention to the fact that Romeo’s romantic language is clichéd, suggesting that Romeo’s feelings might be inauthentic or immature.

O Romeo, that she were, O, that she were
An open-arse, thou a poperin pear! (II.i.)

Mercutio believes that love is grounded in sexual desire. When Romeo makes the romantic gesture of breaking into the Capulets’ garden to see Juliet, Mercutio calls after him that his real motive is not romantic but sexual. An “open-arse” is a slang name for a fruit often compared to the vagina, while “poperin” puns on “pop her in.”

Now art thou what thou art, by art as well as by nature, for this driveling love is like a great natural that runs lolling up and down to hide his bauble in a hole. (II.iv)

Mercutio is pleased when Romeo stops pining for Rosaline. He suggests that Romeo’s “driveling” over his beloved was caused by a sexual desire to “hide his bauble in a hole.” Mercutio doesn’t know about Juliet, but these lines might make the audience wonder if sexual frustration also lies behind Romeo’s love for her.

A plague o’ both your houses.
They have made worms’ meat of me. (III.i.)

When Mercutio is fatally injured, he turns his cynical and realist eye on his own situation. He points out that the feud that has caused his death is pointless. While Romeo and Benvolio talk about Mercutio’s “soul” and “gallant spirit,” Mercutio himself describes his death in strictly physical and unromantic terms: he will be “worms’ meat.”