bilge rat

plural bilge rats

1. Used other than figuratively or idiomatically: see bilge, rat.
2. idiomaticslangnauticalAn insulting term for a dirty, low-ranked, or untrustworthy person.

   hell, he was a bilge rat, never in any port long enough to move up in rank

   1991, Unattributed, “Do you think anybody will come back on Thursday? Should I close the school? Or just leave town?”, in Playboy, page 204

   2 more examples

   He decapitated the man with one blow and continued to chop at his corpse even before it had stopped jerking and rolling on the ground. Like a man berserk, Juan turned and confronted his crew, the blood and gore dripping from his blade which he waved in his hand. “This bilge rat was the one who betrayed us. Let this be a reminder to all of you that no one betrays Panther John. [...]”

   1970, Robert Tralins, Panther John, page 64

   You can't put a price on me first dime! And I can't forgive that thievin' bilge rat Squidward for stealin' it!

   2002, Spongebob Squarepants, season 3, episode 47b "Can You Spare a Dime?", spoken by Mr. Krabs