What grinds my gears? Items that are exceptionally well engineered, but done so in a "silo" environment that doesn't let the engineer see the entirety of the project.
Case in point: 2011 SuperDuty has headlamps that are really easy to change, unplug, 1/4 turn in/out, and plug them back in. However, to get to the point that you're able to get at the the bulb for the swap, you have to remove the entire grill.
2015 Subaru Legacy was just about as bad, had to remove the fender liner to get at the bulb.
2011 SupeDuty, Water-in-fuel sensor is plastic has 2 18ga wires coming into it and hangs down below the frame rails. I've broken 2 of the sensors on snow-drifts. One out on the lake, the other on a section line. Nothing that fragile or made of plastic should hang down beneath the frame rails of any pickup.
Outboard motors. The stupid little rectangle shaped nuts that fit into recesses in the plastic to bolt the mid-section in place. Fine, have the little nuts, but lets make them stay in their recesses a little more securely please.
Suzuki King Quad, you have to pull off a small plastic panel to check the doggone oil. The plastic panel is held in place with those plastic push-pins who's inventor by the way, should've been dipped in honey and staked down to an anthill.
If I were king for a day, every engineer would have to be able to start with a finished product (whatever that is), disassemble said product to get to the part they designed, remove/replace their part, then re-assemble properly. Too much CADD time, not enough wrench time, along with not NEARLY enough time spent understanding the finished product rather than just their little part.