salty dog · noun1
From the salt of the sea. Compare old salt and seadog. Sexual sense may be due to association of sailors with sexual promiscuity, or may be separate development, salty (“spicy”) and dog both suggesting promiscuity.
salty dog · noun2
From being a greyhound (“gin and grapefruit juice cocktail”), plus salt, influenced by existing term.
Etymology from Wiktionary, CC BY-SA 4.0.