忘其所以

Explanation: Defined as the over-excited or proud of forgetting a due manner. 　　Usage: Verb-object type; as the predicate attribute; containing derogatory 　　Source: Ming Feng Meng, "Awaken the common saying Erlang survey documents boots" with instructions from his wife leans over, forget it so. " Thesaurus:  forget, Mo to the poisonous, no one dare harm me— an arrogant boast