The only time I get hit on the head by the safety bar is when I'm wearing a helmet. Sans helmet, my head is small enough that the bar passes harmlessly every time. I'm convinced that the helmet causes the safety bar contacts, and doesn't do anything to prevent injury from safety bar contacts, because the bar would clear the bare head, but hit the helmeted one.
I never initiate the safety bar, but the first thing I do when I get on the chair is position my poles so they don't interfere with the footrest, in case someone else wants to use the bar, so I always get ready for the bar to come down, even before anyone announces it. If no one else wants to use the bar, we ride without it.
Oddly, riding a chairlift w/o a safety bar or driving on Independence Pass doesn't bother me, but flying in an airplane or riding in a glass exterior elevator freaks me out.