I believe early on (70's, 80's) there may have been something in the regs about drinking as I remember one station ops manager having a fit about the talent partying while on the air.
Then again, this thread reminds me of the WKRP in Cincinnati episode where Johnny and Venus drink on the air to illustrate the perils of being impaired by drinking. The officer administering the test was in awe as Johnny's reaction time got better with each drink!
I recall doing a local news program after the Christmas Party at one station I was working it went very well. We watched the aircheck the next day.