1. first thing i notice is their tone. if they walk up to the counter and immediately bark their drink order at me without saying hello. if they throw their money/card at me. customers that are on the phone while ordering don't really bother me that much, it's when they act like their conversation is too important to be interrupted by me asking questions about their order.
2. mostly in the morning because everyone is in a rush to get to work. the weirdos tend to come at close.
3. customers get ticked off when they come in during peak (7am - 9am, when everyone is coming in before work) and we are all sold out of the item that they want. my store is pretty small so we frequently run out of ingredients and food items a lot, so if a customer orders an alternative item and we don't have that either, then they get reaaalllyyy mad.
4. if a customer gets angry when we run out of multiple items, then i can sympathize with them and apologize, offer them anything else that they might want. sometimes i'll give them a discount if the situation really isn't their fault. but if they're just nasty back to me and spew insults, then i'll lose the smile and speak monotone. if i make a mistake on my end and a customer gets angry, i'll do something to make up for it like remake their drink a size up.
5.privileged white men and women. typically they're dressed in fancy clothing.
6. if a customer just shouts their drink at me without saying hello, then i can get a sense of what kind of customer they're going to be. especially when they say it too fast for me to comprehend so i have to ask them to repeat it and then they act annoyed.