If it was interrupted and something was missed or skipped, that does not sound right and it probably should have been done again.

I always make sure to give them my attention, even though I've seen it a thousand times over. More out of respect for the cabin crew, it must be disappointing for them to see so many people ignore it.

I can also recall a flight some years ago where 2 older gentlemen in row 1 were chastised by a crewmember for talking over the briefing, just before the seatbelt fastening demo (arguably the most skippable part). I think he said something like "I need you to pay attention - we can't take off unless everyone's seen it". One of them snapped back, "ok, but you know I could probably do this demo for you, blindfolded".