dirt or dirty laundry

The correct phrase is [dirty laundry], which can either mean, (1) literally, dirty clothes waiting to be washed, or (2) personal affairs which can cause embarassment if publicized.

e.g. 1: His dirty laundry is piling up but he won't wash them.

e.g. 2: We'd better not talk about our dirty laundry in front of our friends.

This phrase is usually used to mean the latter.

*dirt laundry is incorrect as both [dirt] and [laundry] are nouns, and dirt means soil , earth, dust, or mud, while laundry means clothes awaiting washing. The two nouns do not go together as a compound noun.

dirt laundry =臟衣服 dirty laundry= 臟衣物