Question

In Act 3, Scene 1, Mercutio refers to Tybalt as a “ratcatcher” and the “Prince of Cats.” Think about all of the connotations of “cat.” What do you think Mercutio is saying about Tybalt?

Answer 1

I'd say, since cats are known for being stealthy and sneaky, that Mercutio was calling Tybalt, well, stealthy and sneaky. I think the Prince of Cats thing is also an allusion because I remember reading about it somewhere but I can't remember much (eek! sorry...) 
But yeah, I think he was saying that Tybalt is sneaky and stealthy, but also skillful in many ways, and treacherous, to say the least.