I agree with Maxi 101. Being funny, only works if you really are very very funny, and then it only works with one third of the passengers. Everyone else gets pissed off.
You can always tell when you are on a BA flight because the Captain always comes up with some comment about having to listen to important safety information - must be in his flight orders. A few minuits later the purser then also gives a similar announcement -must be in the flight orders. This is then followed by the demo itself - CAA requirement for safety reasons, fair enough.. Surely the demo on its own is adequate.