having an ill or wicked nature; (also) the doctrine that human nature is originally evil (seishaku theory).
儒教では性悪説や性善説の議論が古くからある。
In Confucian thought there have long been debates about the doctrine of innate evil and innate goodness.
彼が性悪だとは思わないが、時々意地悪な言い方をする。
I don't think he's inherently wicked, but sometimes he speaks nastily.