Dream about slapping someone in the face is a metaphor for your innocence, purity, simplicity and carefree attitude. Perhaps somebody is not taking your advice or listening to what you have to say. The path to your goals are not going according to the way you planned it out. It hints a difficult situation that may get your hands dirty. You are coming out of a depressing or gloomy phase.
Slapping someone in the face dream is about your mind may already be thinking ahead to some problems of your life. You are stuck in a routine where you are doing things by rote. You need to keep quiet before you put your foot in your mouth. Your dream is issues you have with getting old. You may be feeling emotionally dirty or guilty and are trying to wash away the shame.
If you dreamt about slapping someone in the face:
Some advice for your diet: avoid caffeine. It is a very prevalent drug in our society, but it may not be right for you. Begin to open your mind and your palette to alternative substances, the most common being herbal infusions, especially green tea. The stress of caffeine on the eyes (vision) can adversely affect you. Also, include fresh fruits and vegetables that nourish your eyes: cantaloupe, cranberries, and blueberries. These delicious food sources certainly taste better than any medicine!