Almost saw someone crash

I wonder if there's an analogy to the drunk driver in this situation?
It's become quite acceptable (and even *strongly suggested*) that
keys are taken away from someone who's impaired by alcohol, or that
a cab is called. Could the same be applied to someone attempting
to fly who is impaired by alcohol?

I realize in the situation initially reported there didn't seem to
be alcohol (or drugs) involved. But what would you do if you
saw someone who was impaired, going to go fly?

And remember -- the car keys situation is a local issue. Flying drunk
is a Federal issue in the US. Don't know about other countries.