be completely indifferent ⇒ 他对妈妈的一番苦心无动于衷。 Tā duì māma de yī fān kǔxīn wú dòng yú zhōng. → He was completely indifferent to his mother's considerable efforts.
言不由衷
not say what one means ⇒ 他的回答言不由衷。 Tā de huídá yán bù yóu zhōng. → He didn't say what he meant.