Not sure that everybody would agree, but: bread maker.
We have one. It's huge, takes up a whole heap of shelf space, and the only thing it does is make bread.
Never mind the fact that bread costs a few pence per loaf in the first place, or that it's perfectly possible to make bread the old-fashioned way. You know, with your hands. I think my real beef with it is that it makes such tiny, tiny loaves, and all with a metal paddle embedded in them. Once you fish that out, the loaf is even tinier.
Sure, throwing some ingredients in a machine and waiting an hour or two is way simpler than the multiple complex cycles of kneeding and rising that manual bread-making requires. But the results are so poor, it hardly seems worth the effort.
PS. Fun fact: First time my mother tried to use her shiny new bread maker, she came back a few hours later to find the bottom of the tin coated in a kind of edible cement. She asked me what went wrong (because, obviously, I would somehow know this?). So I chiselled out a piece of this stuff and tasted it.
"Holy mother of God, how much salt did you put in this?!"
"One tablespoon, like it says."
"No, no -
1 tsp means one teaspoon!"
You do not need a degree in food science to figure out why this might be a problem. ;-)
Funny, you would have thought an extremely old person would know about all the quirky abbreviations in recipies. (E.g., "oz" for ounce? What is that about?)