The self-checkouts at Target where I live are hilariously bad if you are paying with cash. Up to the point where you pay everything is fine, but then if you indicate that you are paying with cash, it says that it is preparing to accept the payment. It takes 20 seconds before it will let you put money in, like there is some sort of data processing it needs to do first. And every third or fourth bill that you put in gets jammed up and you have to pull it back out and re-insert it.
After you put in enough money to cover the amount due, it prints the receipt right away, but it takes another 20 seconds before it gives you the paper money change, like it has to do some more hard-core processing to figure out that 40 dollars minus 37 dollars equals 3 dollars.
The coin change takes even longer, like there is some advanced algorithm it uses to make change that takes it half a minute. Then, as a final "fuck you" to the customer for daring to pay with cash, the receptacle where the change comes out is set up so that unless you put your hand in front of it, it spits half the change out onto the floor.
It's so bad that it doesn't even make me angry any more, it just makes me laugh.
Absolutely just refuse to use the machine. They will accommodate you. If enough people do it then they will get rid of them.
A good example I can think of personally is at McDonalds. It takes 22 finger clicks on the screen to order a medium iced coffee and approximately 140 seconds. There are numerous slow animations, the screens are slow to appear, slow to respond, multiple upsells, positions of buttons change on reflow after clicks. In person it takes "I'd like medium ice coffee light sugar", approximately 7 seconds for that and then the card processing time. Self service is 20 times worse.
Someone else mentioned theft reporting. Having recently spoken with a criminal defense attorney in a social setting, this is an out of control problem. He is in a medium sized city and has seen the number of shop lifting bans increase over 500-1000x. He would typically see a dozen or so per year but since self checkout became dominant in the area he is seeing thousands per year, nearly 1% of the population. This becomes a major problem in an area like this, if you get banned by walmart and safeway you have to travel 2 hours to get groceries, there are no other food stores. There is no recourse, the stores have no interest in trying to resolve these cases where, as the other commenter described, very common human errors resulting from terrible UI are criminalized.