Gomu O Tsukete To Iimashita Yo Ne -

The inclusion of is what makes the phrase iconic. If the speaker just said "Gomu o tsukete kudasai" (Please wear a condom), it would be a simple request.

You might wonder, why is it tsukete to iimashita and not just tsukete iimashita ? gomu o tsukete to iimashita yo ne

– Speaker shifts accountability back to the listener. The inclusion of is what makes the phrase iconic

– A couple or sexual partner recalls a prior agreement to use protection. gomu o tsukete to iimashita yo ne

Readers looking for "angst" or "forced proximity" tropes use this line as a shorthand for the kind of drama they want to read.