| Quote #1
This is about the stupidest reason to start a street brawl ever. (Is there ever a good reason to start a street brawl?)
| Quote #2
Fed up with Romeo's lovesick moping for Rosaline and his claim that he had a steamy "dream" the night before, Mercutio taunts his buddy by saying that Queen Mab must have paid him a visit. (Queen Mab is a tiny fairy that brings dreams to lovers like Romeo and you can read more about her in "Symbols.") Mercutio also informs Romeo that dreams "are the children of an idle brain," which is another way of saying that Romeo is an idiot and his dreams about Rosaline are ridiculous (1.4.12). Given the context of the speech, it seems like Mercutio is suggesting that, like Queen Mab, dreams (especially Romeo's) are small and insignificant.
But Mercutio isn't the only one to point out when his pal is behaving foolishly. Romeo criticizes Mercutio's crazy rant when he yells "Peace, peace, Mercutio, peace! Thou talk'st of nothing."
| Quote #3
Tybalt's all miffed that Romeo comes in to "scorn at our solemnity," i.e. he's shown up to the Capulet ball. But, um, a masked ball isn't exactly a solemn occasion, is it?