Final answer:
The Prince is angry due to three recent street fights instigated by the feuding families of Capulet and Montague which have disturbed the peace of Verona.
Step-by-step explanation:
The Prince in Act I, scene i of Romeo and Juliet is angry with Capulet and Montague because their families have recently started three street fights. This ongoing feud has disturbed the peace of Verona and the Prince has had enough of their quarreling affecting the city. He declares that if such disturbances continue, the heads of each household will pay the penalty of death - showcasing his utter frustration and desperation to maintain order.