In Act 3, Scene 1, of Romeo and Juliet, why does Benvolio think there'll be a fight? And what does Mercutio accuse Benvolio of in lines 15-30?

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sciftw eNotes educator| Certified Educator

Benvolio thinks that there will be a fight because the weather is hot.  

The day is hot; the Capulets, abroad;
And if we meet we shall not ’scape a brawl,
For now, these hot days, is the mad blood stirring.
Benvolio is saying that the hot weather makes people more irritable and cranky than normal, so they are more prone to getting in fights.  I'm not entirely sure if science backs him up on that hypothesis, but I do know that I'm way more irritable on hot days.  
Lines 15-30 are the lines that Mercutio uses to point out that it sounds ridiculous that Benvolio of all people is actively looking to avoid a fight.  Mercutio tells Benvolio that Benvolio is known for fighting people for any reason, no matter how trivial.  At one point, Mercutio mentions that Benvolio once started a fight with a man for coughing and waking a sleeping dog.    
 Thou hast quarreled with a man for coughing in the street because he hath wakened thy dog that hath lain asleep in the sun.
pohnpei397 eNotes educator| Certified Educator

In this scene, Benvolio thinks there will be a fight because the weather is so hot.  He says that in weather like that people always are in a bad mood and spoiling for a fight.  So he tells Mercutio they shouldn't go out.

What Mercutio says in the lines you cite is that Benvolio always wants to fight.  He says Benvolio will fight a man because the man's beard has too many hairs, or not enough hairs.  What he's saying is that Benvolio will fight for any reason at all, or even for no reason.  Because of this, he thinks it's weird that Benvolio wants to tell him how to avoid a fight.