Slightly off-topic, but related.
Years ago I was flying ATL-DCA on an evening flight. Sitting in 1A and next to me was a guy in a blue double-breasted uniform. We talked a bit and I asked if he was navy or public health - he was public health. The FA took his jacket and hung it. Then took orders for PDB. He ordered something alcoholic, a few minutes the FA came back and said she couldn’t serve him what he ordered.
After take off, she returned with the drink and an explanation and apology. She saw the double breasted blue jacket and thought he was a DL pilot. I guess she either looked at the jacket again or checked the manifest and saw he was USPHS.