A customer decided to go to Starbucks whilst her partner went to another shop. She looks me in the eyes as she approaches, is
pressed up against counter, leaning, and as I greet to take the order, tells me to "wait" and just walks off... goes find her partner she knew had gone to another shop and wasn't behind her. 
There is no queue, not that I'd have waited for her to come back before serving someone else. After 3 minutes, having served some customers in the meanwhile, she comes back to order with him in tow... he is paying.

An abrupt "wait! ". Just a single word, not much to go on, not said playfully, jokingly or softly, perhaps she realised she didn't have a means of payment on her. She hadn't attempted to order. Didn't need to approach if she was just checking the menu. Could have said she will be back. Some people are just odd.