In an episode of the television show Archer one character refers to another as being "trout-shouldered."
“This pathetic, trout-shouldered excuse for a boom operator is Chet Manly."
What might this phrase mean?
'Trout-shouldered' presumably means
This probably means that the writer is implying that person so labeled doesn't have very strong shoulders and so is somewhat weak. This is implying not physical weakness but metaphorical weakness of character.
It is not a set-phrase or idiom meaning something outside of its implications.