on one's honor

Idioms  

1. Entrusted to behave honorably and honestly without supervision. For example, The students were on their honor not to consult notes during the exam. Originally alluding to a solemn oath, this idiom dates from the mid-1400s.

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Example Sentences

As a result, politics almost continually involved attacks on one’s honor and reputation…If they got out of hand, it became an affair of honor… There was whole ritual where the offended party asks for an explanation… and then he issues a challenge, and if things don’t get resolved beforehand, which they usually did, it led to a duel.

From Salon

The “tinies” manifest themselves as follows: The tiniest infraction earns an abundance of punishment; the tiniest insult is received as a mortal affront; the tiniest bit of humor at one’s expense is absorbed as an assault on one’s honor — and dishonor must pay a price.

From Washington Post