As SLF I know that any delays aren't the crews fault, they are just doing their job and want to get home on time, as we all do. Much respect, I couldn't do it.
Worst flights I have been on are low cost ones into Newcastle on a Friday night, when half the passsengers are on hen and stag nights and have already been in the bar at the airport.
I have never seen anyone refused entry onto a flight as it seems to me that the ground staff don't want the problems of preventing someone flying.
Maybe all pax should be breathalysed as they hane their tickets over for boarding.