harebrained

1. ADJ You use harebrained 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、理论等)愚蠢的; 不可行的[usu ADJ n] [表不满]

This isn't the first harebrained scheme he's had. 这已经不是他制定的第一个愚蠢计划了。