As a customer, what would you do if a customer service rep lets someone in line ahead of you when it's not their turn yet?

I will do nothing actually. But if it happens the second time around I will get the attention of the CSR and ask him what is the purpose of having other customers fall in line if he will let others bypass us? 

Simple - given the position I am waiting for service (or in line), I may decide to finish my transaction, or simply leave. I would never return to that business, I would find a new place to purchase. 

I have been in this situation, in a jewelry store. I intended to purchase an expensive gold chain.I was waiting my turn to be served.  Some one was ushered in , I was asked to wait while they purchased something considerably less expensive - and took their time about it as well. . 

So, after more minutes waiting ( being now waiting minutes to be served)  I left the store and took my business to another store, as it turned out I got a better deal as well.

I would make sure the person goes to his/her proper position and emphasis on the ethics of Customer service. Every customer should experience a good service at all times so by by passing all the other people they will not have a good experience, so i will make sure i stop it from happening

I won't say anything to that customer but I will give a comment to the related person who is working on this area.

If the reason is just and right, you can ignore it. For example, he may have one item but you purchase full of a trolley, the customer may be old, pregnant, with family and children hard to wait. You also understand this.

If he is in Urgency with Medical Condition requiring immediate attention, will request the Customer ahead of him if he can proceed him prior who has already attended.

My first reaction would be irritation because of the obvious inequity of the situation.  I would think poorly of how the company is handling their staff and on the inefficiency by which they are conducting their staff training. Unless there is an apparent valid reason for entertaining another customer ahead of another in a line, this behavior speaks of immaturity and an inferior staff training administered by the company.

I do anything but on worst case scenario, i may seek clarification as to why he did so. And if the reason is justified, then no problem. But if its not, then he may have to do the right thing or be reported.

I would call a manager to make my voice heard so this can't be repeated with other customers.