It is abuse even when there is a back story that might explain some profound reason to cause the abuse, or when it only happened once. When a teacher uses his/her authority in an improper way, this is abuse of authority in the same way that it is abusive for a police officer to use excessive force. Pastors are abusive when they use scriptures or Gods name for the sole purpose of manipulating emotions. Abuse doesn't require any physical marks. When anyone uses another person to get what they want at the cost of that persons well being, this is abusive. One could even make a case for abuse when a picture or meme is created and shared online without asking permission. Most forms of abuse are socially ignored and tolerated as 'clean fun', but that doesn't dismiss an abusive action.
It doesn't matter if the victim or the abuser is intoxicated during the abuse; misusing another person is always abuse! Sometimes people challenge claims of rape when the victim is unable to remember the details of what happened. While this might sound like a gray area, even this is really clear when looking at the definition of abuse as "misusing something". In situations where one person wants sex and the other person doesn't know if they do or not, any action intended to manipulate that situation is indeed abusive. The act of rape isn't the moment when abuse first occurs and when we stop trying to define abuse by the peak moment of abuse, it all becomes much clearer. In all abusive situations, the abuse actually begins the moment one person decides that they will use another person to get what they want.
Often victims won't come forward with allegations of abuse if they were impaired during the incident, but the mental or emotional state of the victim does not have any bearing on if they were misused by another person.