Final answer:
Vincentio is angriest at the cousin who reveals sensitive information that could ruin them.
Step-by-step explanation:
In the given text, it appears that Vincentio is angriest at the cousin who reveals that he has found out things that could ruin them. The cousin mentions that Vincentio has learned things that could lead to the fall of Richmond if he escapes, indicating that Vincentio is furious at the cousin's actions and the information he possesses.