Leading the enemy against his own people is a pretty severe breach of military etiquette.

To fail to do so was a serious breach of etiquette.

Not to do so would be a severe breach of etiquette.

Talking to more than one isn't a breach of etiquette.

"It seemed a complete breach of etiquette just to be thinking that way."

To the Democratic minority, her presence was more than a breach of etiquette.

To do so would have been an unforgivable breach of etiquette.

A bad move - and a grave breach of etiquette.

In this instance, though, that breach of etiquette might have been acceptable.

A fourth dance would have been a breach of etiquette.