Here's an odd one my wife and I were just talking about. Some years ago, we were redoing our kitchen and the contractor told us to go buy the kitchen faucet we wanted. We went off, looked at several, and picked the one we thought looked the best with what we were doing.

When the contractor went to install it, he opened the box and a battery pack fell out. I couldn't for the life of me figure out why a faucet would need batteries. It turned out that you can turn it on and off by touching it anywhere (handle, faucet itself, whatever), you just leave the physical handle open and set where you want it, then you can touch on and off. I thought it was the dumbest thing ever and we'd never use it.

Flash Forward to now and it's one of the most used conveniences we've ever bought. All those times your hands are covered in raw meat or other cooking mess? Just touch the faucet with your elbow. Rinsing a bunch of veggies one at a time? Tap on, tap off. It works flawlessly, unlike those touchless ones at the airport: no delay and works every time. We will never have a kitchen sink without it - my wife wants them for the bathroom.