noun
insensitive person; cold-hearted person
Refers to someone who lacks compassion or empathy, often used in a critical or emotional context.
彼は困っている友達を見捨てるなんて、薄情者だ。
He's such an insensitive person to abandon a friend in need.
薄情者と言われてショックだった。
I was shocked to be called a cold-hearted person.
冷たい is a more general adjective for 'cold' (temperature or personality), whereas 薄情者 is a noun labeling someone as emotionally cold or unfeeling.
Compound of 薄情 (はくじょう, 'heartless') + 者 (もの, 'person'). The exact historical derivation is uncertain, but the meaning is transparent from its components.