Romeo and his posse (i.e., Benvolio and Mercutio) are getting ready to sneak into the Capulets' party. Luckily, it's a costume party, so they can wear masks.
[We should point out that Mercutio's name was on the invite list, because he's not a Montague, but he feels the need to wear a mask anyway. What's up with that?]
Romeo and Mercutio trade insults and there's some naughty talk about love, in particular, what to do to when "love pricks [hurts] like a thorn." Mercutio's solution? "If love be rough with you, be rough with love. Prick love for pricking, and you beat love down."
Translation: The solution to heartache is to go out and have sex.
Romeo continues to boo-hoo about the unavailable Rosaline and then he announces that he had a dream the night before. Before he can go into the details, Mercutio interrupts and delivers a long, crazy speech about "Queen Mab," a tiny fairy who visits people in their dreams. (You can read more about it in "Symbols.")
Romeo says Mercutio is talking nonsense and Mercutio, our resident skeptic, retorts that dreams are for idiots.
Before entering the party, Romeo says he has a feeling that "fate" may have something bad in store for him.