Why does answer to insults upset mercutio?

Mercutio is upset by Tybalt's insults because he feels that Tybalt is questioning his masculinity and honor. Tybalt has called Mercutio a "villain," a "dog," and a "fool," and has even suggested that Mercutio is not a real man. These insults are especially hurtful to Mercutio because he is very proud of his reputation as a skilled swordsman and a witty conversationalist. He feels that Tybalt is trying to undermine his social standing and make him look like a fool. Mercutio is also upset because he feels that Tybalt is not taking their feud seriously. He believes that Tybalt is simply trying to pick a fight with him for no reason, and he is frustrated by Tybalt's lack of respect.