fēng​feng​diān​diān

deranged

疯疯癫癫 (瘋瘋癲癲) fēng​feng​diān​diān
deranged descriptive
mentally unstable or behaving in a wild, uncontrolled manner

Ever since he suffered a major blow, he has become mentally unstable.

erratic descriptive
acting in a silly, flighty, or unpredictable way

That child runs around wildly all day, never being serious.

Frequency

Movie subtitles
2.21 per million appears in 1% of films
Written text
0.726 per million

Sources

Definitions
CC-CEDICT