And sometimes they (particularly YX) say why they aren't going to do it, other times they just don't do it. My favorite version was "As a reminder, in the event of a loss of cabin pressurization you will need to remove your face mask before consuming our complimentary oxygen"

IIRC, the life vest/flotation means technically is only required for overwater flights. It drives my wife batty to no end that they never (even in the taped demos) actually inflate the vest.