屎坑關刀——文又唔得,武又唔得 [--关------------]

Jyutping si2 haang1 gwaan1 dou1 — — man4 jau6 m4 dak1 , mou5 jau6 m4 dak1
Pinyin shǐ kēng guān dāo —— wén yòu wú dé , wǔ yòu wú dé

Definitions (Wiktionary)
  1. phrase, Cantonese, idiomatic
    to lack ability and be useless