There’s a reason John Watson gets into rows with chip-and-PIN machines.
It’s not that they don’t like him, really. It’s that they soak up so much from every person who touches them. Every fingerprint carries a little bit of its owner, a little bit of their life and whatever mood they’d been in while doing their shopping. And John has a tendency to, in his turn, soak all those bits up from the machines. It’s not that he wants to, because he doesn’t. He hates it, but you can’t build mental walls against machines.
He knows. He’s tried.
Electronics are funny creatures, though. They don’t have feelings, but they certainly seem to resent when he steals all those little bits of all the people who’ve used them before him; they go wonky.
If John took the time to think about it, he’d likely come to the conclusion that there’s some sort of electromagnetic something or other science-y (and wouldn’t that make Sherlock wince and launch into a three hour lecture) that would explain why they all go wonky on him when he touches them, but that would require he not yell at the programmed voice and keep his cool about it going wonky. Again. Every time.
John gets mad at chip-and-PIN machines much more easily than he gets mad at anything or anyone else. Including his sister.