You are right, it is a masterpiece!
Stanley Kubrick was known as a perfectionist and a control freak, but he was ALSO known to let his actors improvize if he thought it worthwhile.
It certainly was in the case of Ronald Lee Ermey, and he made up many funny lines in this movie.
Stanley Kubrick was said to be bursting out in laughter of his perfomances from the sideline, and I wonder if this may be the worst insult ever:
"Bullshit. It looks to me like the best part of you ran down the crack of your mama's ass and ended up as a brown stain on the mattress."
As for the commercial being banned; I have no idea. Beer commercials are illegal in my corner of the world, but it would surprise me if they are in the US.