► 形容詞甚だしい  [(5)はなはだしい]  [liter]    
meaning:  excessive  rank: 3☆ 
無責任も甚だしい ⇨ That’s excessively irresponsible
More examples:- 全く傍迷惑も甚だしい ⇨ 
 - 責任感の甚だしい欠如 ⇨ Egregious lack of responsibility
 - それは公私混同も甚だしい ⇨ That is an outrageous example of mixing up public and private lives
 - 現実からの乖離が甚だしい ⇨ That’s far away from the reality