“Tuned to the particular typing mistakes to which Teitelman was prone”

Recently, I asked on social media, “Is there a UX design equivalent to this?”, and attached this photo: In case you don’t know, this is a (mythical) male-to-male power extender. Requests for those seem to spike around Christmas, and the reason is this: if you put up your lights, chain them together, and only then realize you did it in the wrong order – with the holes next to a socket – it seems much easier to imagine using this cable than reversing all the lights. There are apparently other uses, like powering your whole house from a portable generator. But I don’t know if you can actually buy such a cable. What I do know is why you wouldn’t want to buy one. The cable has a horrible flaw that might not be immediately obvious: once you plug it in, the other end now has exposed live wires that can electrocute someone. So, my question was really: What in design has a similar property? What’s something that seems like a good idea, but is actually pretty bad and/or even dangerous? I would…