Turkish customer who don't know Western Culture/Etiquette

Great start to the morning....

So I was doing a transaction for customer A at the counter, but then 3 other customers come into the store and stand around the counter waiting to be served. Some ppl have no etiquette, if you see someone at the counter, paying money and asking for medical advice, stand aside. Don't stand smack bang in the middle or next to him and listen to our conversation. 

Anyway, when customer A leaves, I see customer B, C and D standing around. Both B and C were next to each other at the counter. I didn't know who was first so I asked before serving

Me: "Sorry who's next?"

Customer B: My money is on the counter, of course its me!!! (looks angry)

Customer C: Dunno, probably her.

Me: Ok 

Customer B: Of course its me. I'm here first.

Me: I was only asking who's first. I don't know why you are so angry.

Customer B: Didn't you see me standing here??

Me: No I didn't notice because I was serving another customer. Look I'm only trying to help. (me rolls my eyes)

Customer B starts to say @#$#$@$@% in her language (Turkish) to Customer C and Customer C reluctantly nods. And Customer D overheard and started to says stuff (sounds like defending me). 

Me: So you're first right. Fine. Sign there.

Customer B signs and pays and says stuff in her language and walks off.

I serve Customer C and apologised for the situation. 

I serve Customer D and he tells me what she said in Turkish:

"She said you treat her like shit all the time, but don't worry about her, don't let her ruin your day."

Me: "I don't even know who she is! Anyway, if you call asking a simple question is treating her bad, then there's something wrong with her. I won't let her ruin my day, she's just a little nobody."

We both laugh.....

Stupid racist old lady. In western culture, people line up to save confusion. But in your culture, you stand around like you're king shit, of course retailers will ask who's next. Don't chuck your money on the table when I'm serving another customer. Wait til that customer finishes. Oh and please stand aside. 

I don't get it. If i don't ask, and I serve the wrong customer, you're gonna complain you're first.
If I ask before serving, you still complain..... Maybe there should be a third option i.e. don't serve you at all and not do your business.