Consider: 半吊子

Wiktionary

Noun
半吊子

1 (figuratively, colloquial, derogatory) one who lacks adequate knowledge or skills; dilettante; smatterer; dabbler
2 (figuratively, colloquial, derogatory) hot-headed or impulsive person; one who leaves tasks unfinished, or the tasks which are unfinished

Consider: 半吊子

Wiktionary

Noun
半吊子

1 (figuratively, colloquial, derogatory) one who lacks adequate knowledge or skills; dilettante; smatterer; dabbler
2 (figuratively, colloquial, derogatory) hot-headed or impulsive person; one who leaves tasks unfinished, or the tasks which are unfinished

Example from English du jour - online English classes available on Facebook

每日英語 : 海夫愛司 half-assed=[半吊子 <Everything he does, is half-assed. 他做什麼事情都半吊子。>]