He racked his brains trying to ingratiate himself with the boss.
Tips
usage
Often carries a faintly negative or sarcastic tint - suggests effort spent on dubious goals (flattery, schemes, loopholes). Neutralized by context. Common frame: 挖空心思 + 想/要 + verb.
memory
Visualize 挖空 (hollowing out) your 心思 (thoughts) - scooping your head empty to find one more idea. The physical image of exhausting every corner of your mind makes the phrase stick.
