Don’t say it with ~てはだめだ


Grammar Explanation

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Syaro gives a vague account of her first meeting Rize, as the truth is too embarassing for her. When Cocoa misunderstands the event, Rize prepares to tell what really happened.

シャロ:
「あっ()っちゃだめです!」
“Ah, don’t say it!”

Note that ちゃ is a casual spoken variation of ては.