United States Postal Service at 2319 Nostrand Avenue, Brooklyn, New York.

Hands down the worst post office that I have the displeasure of having to use for my business. The counter staff is extremely hostile and lazy.
I went in because my package said it was delivered (I wasn't notified because they are too lazy to ever deliver and rather leave me slips instead) and was told it wasn't there without the clerk even checking. I asked her to ACTUALLY check. She disappeared for 20+ minutes as I listened to her have a fun conversation with her friend in the back until she returned with of course my package in her hands and the bitter look of being proven wrong pasted on her face.

How it could improve: fire everyone, tear down the building, and replace it with a garbage landfill because even that would be a step up from what it is right now. Daycare for miserable adults :)