Ok here's one, it was when Aguirre talked about "stemmin' the rose".
#1 I had no idea what that meant...(but I had an idea)
#2 Why would Aguirre know what that was?
Well, Annie Proulx said that when she was interviewing a ranch foreman/herder boss, he said something like "we send two up together so they can poke each other when it gets lonely". (Although I wonder if he was exaggerating/embellishing that for her, since she was angling for info about rural homoeroticism... but that's another conversation.) In such isolated male-only work environments, quick mutual "relief" may not have been such an anomaly. But Aguirre was still disapproving in this case, since J + E's romantic horseplay went far beyond that.
How would Aguirre know or have that terminology? In the manual-labor world, guys can jabber on all day while working (such as Timmy the Asphalt Guy) and every conceivable subject comes up... Ennis later says "I hear what they have in Mexico for boys like you". Same deal.