From what I witnessed, the guy stepped away from the window after getting his money order for half a second to grab something (a pen maybe?), but still needed to ask the employee a question and had communicated to the employee that he still needed help. The employee told him to get back in line (knowing this post office, it takes 40 minutes to work through a 5 person line).
The person got upset, but the worker started cussing him out first, and after the guy left the worker continued to talk about what an "asshole" the customer was and "fuck that guy!"
This is the same post office where they have interrupted a customers transaction in order to allow their friend to check out with his package ahead of the entire line. And yes, I complained and literally nothing came of it.
I attempted to call USPS just now, and the phone line says "customer service is not available".