So one of the coolest co-workers my father had was a recon pilot during the Viewnam War. Not doing the high altitude picture stuff, but SIGINT and comm monitoring over the radio stuff.
He volunteered and went to Nam for the Navy. He was sent to schools stateside to study Vietnamese first, since he did well on the ASVAB, or whatever the hell it was then. While studying with Vietnamese, in DC I think, they would play cards and learn to talk. His first mis-step was crossing his legs, putting one leg on a knee, and showing his instructor the sole of his foot. Super offensive apparently, and off to a more boring instructor he went.
Then, once he was in country on intel flights, almost all of the people in the bases were South Vietnamese, but he is trained to speak Northern, for less than obvious reasons. So this got him into trouble routinely, and made him an issue with on-base stuff. One woman, a cook, on his first day was in the room and he asked "How are you, sister?" In Nothern, this is fine. In Southern, he called her a slut or a whore (someone can back me up on this). She ran out crying, and they needed a new cook.
He said he caused a lot of problems like that. That was the first time.