I have literally ripped a seatbelt and it's fittings out of the plane I was riding in at the moment of impact. They found the seatbelt still bolted to a bit of ripped out airframe the next day. Prior to that, and still, I have very little sympathy for passengers who do not wear their seatbelts when they can and should. If a passenger is seated next to me, I'll politely ask them to buckle up if they undo. I have a lot of empathy for cabin crew members who must be unbelted for so much of every flight.
The only very historic exception to this which I was told about, an oldtimer pilot mechanic was flying four people in a Cessna 180 floatplane. They were going down into trees - it was going to be messy. The pilot yelled back to the two back seat pax at the last moment to open their seatblets. Stunned at the demand, but with no time to inquire, they complied. They were injured in the crash. But, the floats were ripped off the plane entirely. What the pilot suddenly thought about was that the back outboard seat belt fitting were bolted to the float attachment fittings. When the ripped off floats were found, the outboard seatbelts were found with them, rather than still in the fuselage. The design has been changed, and when I approved seat belt installations, I consider very carefully what part of the airframe the seatbelt fittings are attached to!
But, these days... Just wear your seatbelt!