As a PPL I've had a couple of problems giving safety briefings. On one occasion I forget to tell the passenger where the sick bag was, to have him say afterwards that he'd spent the whole flight worrying about being sick in the absence of a bag. That was clearly my failure, as I had been trained to brief about the sick bag.
On the other occasion I failed to tell the passenger that I knew about the weather coming down from the north and had prepared a choice of three airfields to divert to further south if necessary. He told me afterwards he'd spent the entire flight worrying about what would happen if we couldn't land back where we started.
Clearly if one takes someone up for a joyride one doesn't want them wasting the whole flight worrying about something unnecessary because you didn't brief them about it. But how do you predict what they're going to worry about?
I can only think to add to the briefing "tell me at any time if you're worried about anything no matter how silly you might think it is". What do the professionals think?