let someone down—disappoint a person; fail to support or aid smb.:
- I leave it to you, Stephen. I know you’ll not let me down.
Note: The expression is not antonymous in meaning to the phrase let up on someone—treat a person less harshly or severely:
- By the time Jon turned eight, our financial problems became so overwhelming that I began to let up on him.
let someone down easy —(also: let someone down softly) treat a person considerately so as to spare his self-respect:
- The fact is, and I hope you would respect and appreciate this, I care for him enough to let him down easy.