an expression to criticise someone doing something that they shouldn't be doing, when they should have been doing something else [colloquial]
Definitions (粵典–words.hk)
語句
批評某人唔去做應該、需要做嘅事，偏偏做啲唔應該、唔需要做嘅事（亦係歇後語「年卅晚謝灶」嘅下半句） a criticism of someone for not doing what is needed but instead doing something unnecessary, also the latter half of the sandwich pun 年卅晚謝灶; literally: what should be done is not done
你好做唔做走去搞佢做乜？
你好做唔做走去搞佢做乜？
nei5 hou2 zou6 m4 zou6 zau2 heoi3 gaau2 keoi5 zou6 mat1? Why are you bugging him instead of getting something useful done?
Examples (粵典–words.hk)
Cantonese
好做唔做
好做唔做
hou2 zou6 m4 zou6
a criticism of someone for not doing what is needed but instead doing something unnecessary