The Alfa Guilia coupe and saloon rear suspension bump stop. A rubber section bonded (allegedly) to a steel base, then they use a spacer in raw aluminium with no barrier of any kind. When the rubber falls off, the steel bolts have had galvanitic corrosion with the aluminium spacer, which means that it takes forever with a hacksaw to cut through as there isn’t really space to get an angle grinder in.
Or, on the same vehicle, putting the brake master cylinder in a very poorly sealed box under the footwell floor, right in the firing line of any spray etc. From the offside front wheel. This means that within a very short space of time the master cylinder gets crap in it and fails. Then, because the brake system has two remote servos, both quite a lot higher than the master cylinder, you have to use a pressure bleed system to get a firm pedal, and even then it is a right pain.
I loved the three GT juniors I had, right up till the time they had brake failure.