ともあろうものが

expression

of all people; a person of ...'s standing

Used to express surprise, disappointment, or criticism when someone of a certain status or reputation does something unexpected or inappropriate. Often follows a noun describing the person (e.g., 先生, 警察官).

• 先せん生せいともあろう者ものが、そんな間ま違ちがいをするなんて信しんじられない。

  I can't believe that a teacher, of all people, would make such a mistake.

• 警けい察さつ官かんともあろう者ものが、スピード違い反はんをするとは。

  A police officer, of all people, committing a speeding violation!