It's a tough one. Sure, people fly alot more these days but even so, most passengers would hesitate and ultimately be unsure of their actions. Of course, just refreshing the information by watching the briefing can help.
Adding humour into the demo is a great idea and people have tried it. IMO it works. However, some passengers (admittedly a minority) do complain about this. Some would argue that crew aren't comedians and that only certain people can pull it off............there shouldn't be pressure on others who can't.
Also, you have to realise that many airlines do not like such behaviour during the demo. My airline is probably one of the carriers that many of you would think advocates such humour on the briefing due to it's fun and orange culture but in actual fact it's a big no no.
As for trying the lifejacket on, i would let you but I can also understand the "creating panic"/"causing a distraction issue". But to be fair, if you watch and listen to the instructions on the demo, there isn't any need to try one on. It's designed to be very simple.