I come in with my girlfriend and grab some stuff. I walk up to the busy counter. Two open registers, both with customers at them. There was a dude in a white shirt just sorta waiting before us in the now cluster that is the line. But he walks off and starts shopping again. Leaving me and my girlfriend alone waiting. 
Then a different dude and his girl come up and just sorta stood next to us. So once again we are in a cluster. 

Now this next part happens sort of all at once:

One customer is done at a register leaving one open, that cashier turns around and appears to stock something, man in white shirt comes back and stands NEXT to the new guy and his girl. 

We are now in a parallel line to the counter. All just standing awkwardly. 

Now at this point I assumed we were first. Right? 
Now, I have social anxiety so I even still waited to see if someone else wanted to go first. None of us moved so we just went ahead. You know, get this ball called "life" rolling.

As we walk up the cashier gives us a smug look. 
She says I shit you not.

"I think you cut some people, that was rude"

I said "uh, no I think that's a misconception". 

I turn to the other guy and his girl. I asked him if he was standing there longer than me and he laughed and said no. (at this point the man with the white shirt moved to check out at the now second open register)

The cashier said she was referring to the dude with a white shirt. Which I then said (which I regret kinda)

"He was standing here, but he went and grabbed some other shit while you were busy with someone else"

She smirked and said nothing. Shoved the receipt in the bag. Everyone knows what's going on. Even the dude in the white shirt. I stand there and my girl grabs the bag and tells the cashier to have a fantastic day. 