For me, it's the once used pasta machine that I was so keen to get my hands on. My dad bought it for me...I made some fancy bow shaped pasta and haven't used it again since (about ten years ago).
Same for the ice cream machine from Lidl last summer. I really wanted it. Made ice cream twice, it was rock hard both times :( Never used it since.
Also have a juicer. Random gift from my dad. Lives in the cupboard of doom. Never been out further than to look at it.
Ooh...annnnnd, I bought a cutter thingy for a whole pound not long ago, to make veg into fancy shapes. That's been in the cupboard of doom since too.
There is probably more tbh.
What about you lot?