Why I don't bitch out employees, as a customer.

Two reasons: first, I'm not an asshole; and second,

think about the purpose. This is communication 101. Or manipulation 101, if you want to take it that way.* What is the purpose of communicating with this person? 

Are you: 

1. Trying to reach a material goal, i.e., acquire a service you believe you're entitled to?

2. Trying to express your anger? (To what end?)

3. Trying to make the other person feel bad? (To what end?)

Reason 1 has a tangible goal, one that can be communicated to the other person in a way that they can act upon, or at least respond to. This is generally a shared goal, at least in category or context, as generally employees are there in a helpful capacity. 

Reasons 2 and 3 need further questioning. What are you trying to accomplish by expressing anger? 

Is it the thing stated in reason 1? Then the expression of anger is not the goal, it's that tool you're choosing to use. It's pretty ineffective and wastes a ton of energy, but there's a chance a compromise can be reached; you just have to accept being known as an asshole, and thereby you should expect people to go out of their way to be unhelpful in the future. 

Is it just that it feels good to vent your anger? Why? What do you accomplish when you do this? Do you feel seen? Do you just want people to know how much you're hurting? Again, this method is pretty ineffective and wastes a ton of energy, and you should expect people to go out of their way to be more unhelpful in the future. 

Do you want to hurt the other person? Why? Think their 'stupidness' should hurt, so you will be that hammer of justice? Or do you think they're 'doing this' on purpose, and you need to hurt them back? Why? What does that accomplish? So now you're both upset and hurt and angry? So now you'll actually be able to reach an agreement? ...Do you really think that's how people work? - I didn't think so. 

If your goal is to acquire service, it's very easy: be kind. It takes much less energy, there's no hypertension involved - perhaps disappointment, but nothing an adult can't handle, right? Right?

Right.

*That's a whole nother conversation.