いたずらじゃありませんでした
悪戯じゃありませんでした
itazurajārimasendeshita

Noun
Desu Copula
na-Adjective

The polite, past negative form of いたずら

1. It wasn't a prank.; It wasn't mischief.; It wasn't a joke.

Past/Perfective
Negative
Polite
Terminal Form
Usually Written in Kana