Some customers are super troll-like. 
A man approached to order a flat white with the phrase "Can IIII ____  just have ___ aaaa ____ flat white ____ with oat milk?"
The words "just" and "a" normally implies singular!

I then go through the flowchart of asking for the customer name... before he adds "Oh, ____ annd ____ a tall Americano ___ black". 
Nothing wrong with a customer adding on another drink. I always upsell additional drinks, modifications or food unless they use the keyword "just" as it is just annoying for the customer to be asked after stating they just want the one drink or food item. That certainly annoys me anyway.

What was annoying was the drinks just kept getting added...
"_______ annndd ______ a cappuccino"
"____ a regular Latte" 
At this point I am thinking this is a prankster, especially using the word tall but not grande for the latte, and seems like a sweep of the menu. He isn't on a phone call and has no earbuds in.

" annnnd another ____ flat white ____ two flat whites"
I'm getting annoyed (even if just internally) with the elongated "and" used by him.

He finally ends up with just the one more drink...

"a large Cookies and Cream Frappe"
There is no way he is ordering 6 drinks just for himself. I confirmed the drinks and my hunch on two flat whites rather than two additional flat whites seemed correct. He paid by card, no issues. How is he even going to carry them?!

No attempts for a refund or to make an issue with any of the drinks made, makes me worried that he was using someone elses card. I carried on with the busy period of customers over the next 90 minutes, not sure what happened with the drinks, I presume others came for it.