Always Sunny In Doucheville

Is the weather always good in the city? 3

I've seen this picture a few times as a joke: if you wear sunglasses, you should, because the weather in the city is always good. I don't know what that means. I think there is a cultural aspect to it and I am not American. Can anyone help me find out? Thanks for being more clear. Thanks in advance

There is a sunglasses in the bag, ordinary people wear sunglasses in the sun, there is always fun in the city. Basically, bags should always wear sunglasses no matter where they are or what the weather is like outside.