It's a joke. The city of Key West is its own worst enemy.

The endangered gray nurse shark is its own worst enemy.

Complacency is our worst enemy.

[The city has come a long way from its image in films like the 1983] Terms of Endearment, ... must be from New York.

When you look at yourself you will find your worst enemy. Maybe not literal but it is very typical.

The worst enemy women have is in the pulpit.