Extreme bill-allocation fail

This happened at lunch on Thursday, with weegoddess, at the Pizza Express near King's Cross.

Perfectly acceptable food, then the time came to go; she asked one of the staff (female, early 20s) for the bill. It arrived facing me. Time came to pay, we did some of the obligatory cash-faffery, she tried to get a 20 split at the till, didn't work, eventually decided to put it on her card and take my share in cash - all perfectly normal. So weegoddess attracts the attention of the same staff member, asks if she should take her card over to the till; the staff member says, as you'd expect, "no, we have a machine, I'll get it". When she returns, the card is on top of the bill on its little saucer; she starts running it, I look away so as not to see any numbers - and then she tries to hand me the machine so I can type the numbers in.

I haven't seen anyone get it that aggressively wrong in ages; it's really annoying.