noun
contrary person; sourpuss; dog-in-the-manger
Describes someone who habitually takes a negative, contrary, or uncooperative attitude; often used for a person who refuses to go along with others or spoils things out of stubbornness.
彼はひねくれ者で、みんなが賛成すると必ず反対する。
He's a contrary person; whenever everyone agrees, he always objects.
あのひねくれ者
That sourpuss ruins the fun atmosphere for everyone.
あまのじゃく is a more literary or traditional term for a contrarian, often with a mischievous or folkloric nuance, while ひねくれ者 is a straightforward description of a stubbornly contrary person.
へそ曲がり is a colloquial, slightly milder term for a person who is perverse or contrary, often used in a teasing way.
Compound of ひねくれ (continuative form of ひねくれる 'to become twisted/perverse') + 者 (もの 'person').