bat country

Las Vegas is a city buzzed with nite life activities (gambling and big shows). Bats are norturnal animals, hiding in caves during bright hours and come out roaming for food in dark hours.

A dark country or a dark county both refer to a place bustling with night life. This is probably why Las Vegas has been coined with this name.

供参考：

He batted the idea around in his head.
他脑子里反复思考这个想法。

The cat batted the balloon with its paws.
猫用爪子击打气球。