You are a cashier" from "Seinfeld"
MARLENE: Well, okay. I guess things changed for me on Tuesday night.
JERRY: Tuesday night? What happened Tuesday night?
MARLENE: I saw your act.JERRY: My act? Wha-What does that have to do with anything?
MARLENE: Well, to be honest, it just didn’t make it for me. It’s just so much fluff. JERRY: I can’t believe this. So what are you saying? You didn’t like my act, so that’s it?
MARLENE: I can’t be with someone if I don’t respect what they do. JERRY: You’re a cashier!
What does "you are a cashier" mean in this context?

Question

You are a cashier" from "Seinfeld"
MARLENE: Well, okay. I guess things changed for me on Tuesday night. 
JERRY: Tuesday night? What happened Tuesday night? 
MARLENE: I saw your act.JERRY: My act? Wha-What does that have to do with anything? 
MARLENE: Well, to be honest, it just didn’t make it for me. It’s just so much fluff. JERRY: I can’t believe this. So what are you saying? You didn’t like my act, so that’s it? 
MARLENE: I can’t be with someone if I don’t respect what they do. JERRY: You’re a cashier!
What does "you are a cashier" mean in this context?

Answer

Someone who works in a shop, at the till, dealing with customers purchases. Usually not considered a very technical or respected profession. Here Marlene says she can't be with someone she doesn't respect and Jerry implies that Marlene is not worthy of respect either as she works as a cashier.