As SLF, child of a now retired pilot, I always keep my seatbelt on & have flown through bad turbulence in the past & it never ceases to amaze me how many PAX don't wear their seatbelts.
I've preached to my neighbours around me about keeping it on. But from my point of view, the emergency briefing is often ignored as it's always done in the same routine on every flight on every type of aircraft.
Maybe if trainers were a little ingenious about emergency briefing to change it, make PAX sit up & think there may be a little more concentration on it AND for CC to explain & demonstrate at the end; KEEP your BELT FASTENED LOOSELY throughout the flight!
Show a couple of simulated videos to PAX about what can happen whilst flying through turbulence during taxi-ing - radical but could be effective!
Arik