Wanderin Star - absolutely true about Cabin Crew in the safety briefings. BUT...
If there ever was a problem, we the pax expect the cabin crew to do their utmost to protect us, at the ultimate cost to them if needs be (thinking Man Airport 737 here). If the CC have some fun at briefing time, then OK, but I know that if we got into difficulty the professionalism & bravery would be there.
However, if pax cannot be bothered to listen to simple instructions yet they still expect the ultimate should there be any problem. then why should any CC put themselves out. I agree with OzzieO & Skysista - the expectations of your company & the other pax are on you here and if that is the mechanism you need to get the message over then do it.
OK, so I no longer think you should take one pax to the front and kill them as an example to the others of what happens if you don't listen, but maybe adding a dummy to the kit you use, and then beating it soundly round the head to show what happens to pax who don't listen could be a useful addition to the safety breifing?