| Quote #1
Sampson doesn't have a good reason to insult the Montagues' servants – he's basically looking to stir up trouble because his masters (the Capulets) are feuding with the Montagues. The funny thing is, Sampson's too much of a coward to own up to his silly gesture because the "law" won't be on his "side" if his thumb biting causes a big old brawl (he doesn't want to get busted for causing a fracas).
It doesn't get any more ridiculous than this, folks, which seems to be Shakespeare's point. The Capulet/Montague feud, which has obviously trickled down to involve their servants, is completely absurd. Just like Sampson's thumb biting.
| 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 is quite the bully, don't you think? He's also incredibly rash – after spotting Romeo and the Capulet ball, he calls for his sword and is about to pummel Romeo, until Lord Capulet steps in and calms him down, that is.