I've heard that while in the Marines.The one I haven't seen is " Shines like a diamond in a goat's ass". Is this considered Military jargon or just some inbred Rowley saying, and what the He'll does it mean?
It means that among a group of people, that there are non-performers (the goat's ass) and also a person who is the exception (the diamond).
The exception stands out.
(Now, standing out among the group in a military context may or may not be in a person's best interest.)