mean-spiritedness; base character; vulgar disposition
Refers to a person's innate pettiness, spitefulness, or low-minded nature. Often used as a strong insult or criticism of someone's character.
あんなことを言うなんて、下種根性が丸出しだ。
Saying something like that really shows your mean-spirited nature.
彼の下種根性にはもう我慢できない。
I can't stand his base character anymore.