1 Mercutio: Okay, we need to get this body out of the street. Give us a hand!
2 Jack: Why? This is London. There are always bodies in the street.
3 Mercutio: Well... maybe so, but not ones you’ve had a hand in killing.
4 Jack: Oh, I wouldn’t say that, exactly...
4 Mercutio: Just help us, okay!

I did consider having Jack say, "This is 16th century London. There are always bodies in the street." But then how often do you hear people specifying the century they live in (other than to complain about the lack of flying cars)?

It would have been more believable to have Jack say, "This is 16th century London. Where are the flying cars??"