ADJ-GRADED [usually ADJ n]（计划、理论）愚蠢的，不切实际的 You use hare-brained to describe a scheme or theory which you consider to be very foolish and which you think is unlikely to be successful or true. （计划、理论）愚蠢的，不切实际的 [disapproval]
This isn't the first hare-brained scheme he's had.