When you get a particularly angry customer, kill them with kindness. It drives them a lot more crazy when you smile and sweettalk than when you stoop to their level and get mad back. (This also works in traffic-someone flips you off, smile and wave. They honk their horn? Blow them a kiss!)
Example:
Cust-I’ve been waiting 45 minutes! What are you, stupid or something??
Cashier-Oh my goodness, I’m SO sorry you have had to wait, but thank you for being so patient! (big smile) I’m just doing the very best I can, it’s just hard to give everyone great service when you’re rushing through them…
At this point, either the angry customer sighs heavily and waits some more, or they leave (one less link in the line), or the rest of the customers pile up on him, and he really feels like an idiot.
Other than that, just take it one customer at a time, as I instruct all my new cashiers to do. The line is what it is-if you worry about the guy leaning against a wall and looking at his watch 30 people in, the first 29 are going to get lesser service.
Be patient, go at your own pace. Once you learn the register, the job will be a hundred times easier. Until then, smile, and apologize if you make a mistake. Your customers are all human-they’ve all been new at something at some point in their lives, and most will cut you some slack.
Oh, one last thing-if you do get that particularly angry customer who wants to get up in your face and yell, get a manager over there. You probably don’t get paid enough to take that crap. That’s why managers make the big bucks-we get to deal with the hard stuff. And, managers usually have more power to make them happy again, to keep the customer. Pass the buck. It will make your life a whole lot stressful.