It looks as if Prince Andrew's reference in his Newsnight interview to Jeffrey Epstein behaving in a "manner unbecoming" may be an expression he picked up in the royal navy.
I was recently watching the film "A few good men", about a court martial of two US marines for murder and "conduct unbecoming" of a US marine. It reminded me of Prince Andrew's Newsnight interview:
PA: ... Do I regret the fact that he has quite obviously conducted himself in a manner unbecoming? Yes.
EM: Unbecoming? He was a sex offender.
PA: Yeah, I'm sorry, I'm being polite, I mean in the sense that he was a sex offender. ...
www.bbc.com/news/uk-50449339
"manner unbecoming" appears in the Armed Forces Act 1971:
The following provision shall be substituted for section 64 of the Army Act 1955 (under which an officer who behaves in a scandalous manner unbecoming the character of an officer and a gentleman is to be cashiered):—
www.legislation.gov.uk/ukpga/1971/33/par...ous-offences/enacted