This happened yesterday, it wasn't super busy, but customers would come in bursts that lasted for quite some time. Naturally, so the people in line wouldn't wait too long, I moved quickly and tried to make sure things went smoothly as possible.
A man came to the register with a bag of dog food and a few other items, which he set on the counter. Before I could even greet him or ask for his club card, he noticed the dog food bag has a tear.
Man: Can I just run and grab a new bag?
Me: Not a problem! I'll hold your other things here.
There was another woman in line, who only had a single item: a bag of dog food, already flipped in the cart so the UPC was facing me. She was the last one in line (for now), so I figured I could help her quickly, so she wouldn't have to wait, and the line wouldn't grow if more people showed up while we waited.
Me: Hi, I can help you if you're ready!
Woman: Uh...are you not going to wait for him?
Me: If you'd like to wait, we can, but he will be a moment and it didn't seem like you had much today!
She stepped forward and we had a quick transaction. The man came back as I was handing the second customer her change.
He glared at me, and I was taken off guard for a moment.
Woman: I told them to wait for you!!
Me: I'm sorry sir, it's nothing against you! It's been a little busy and I wanted to keep things moving. She only had one item, and we're already done, I can help you.
He didn't say anything more, but was a little more stern through the whole transaction, still polite, just not as friendly. I apologized again, but still didn't feel like it was that big of a deal.
I asked my store manager later, and she agreed that most people wouldn't have been so upset by that, and that I was just being efficient. Part of me still feels like I might have done something wrong, but I know I've done similar things with no issues.
And, as expected, when I was done with his purchase, there were 3 more people in line anyway.