person who talks constantly about his profession or usage of jargons (idiom)
Definitions (粵典–words.hk)
語句
同人交談，唔理係咩場合、咩對象，硬係會提返自己做嗰行嘅嘢，話題總係離唔開自己嘅行業 to talk shop; literally: never make three utterances without touching on one's profession