I’m not sure when car manufacturers started making seat belts in the backseats of cars not interchangeable, but it has to stop.
If you’re not familiar with this, find a car built in the past few years and see if the passenger side backseat belt buckle can fit in the receptacle on the driver’s side of the backseat. Most likely, it can’t. I assume this is some sort of affordance that car designers have put in place to “help” passengers figure out which seat belt buckle fits with which receptacle. Googling hasn’t returned any decent results as to why this design decision was made.
My gripe is that the safety gains from enforcing one buckle to one receptacle do not outweigh the inconvenience of trial and error when trying to buckle up in the back seat. Beyond just inconvenience, though, bigger individuals can’t use two seats this way, because the middle receptacle won’t accept a side seat belt buckle.
Obviously, this is a minor thing and definitely a first world problem, but being related to design and engineering I felt like it was appropriate material to cover.