A colloquial, somewhat old-fashioned noun for a lecherous disposition or persistent lewdness. Often used in a critical or humorous tone.
That guy's lecherous nature is completely exposed.
Rare extended use: a greedy or self-indulgent mindset, often with a nuance of shameless desire for gain. Less common than the lechery sense.
He's only thinking about making money out of sheer greed.
Compound of 助兵衛 (すけべえ, a colloquial term for a lecher) and 根性 (こんじょう, 'disposition' or 'spirit'). The exact origin of 助兵衛 is uncertain, but it is likely a playful or euphemistic kanji assignment to the older word すけべい.