It's important to note that physical violence is not an appropriate or acceptable way to handle conflicts or disagreements.
If you slapped an elderly man across the face, it could be considered assault or battery, depending on the laws in your jurisdiction and the severity of the incident. Regardless of the circumstances, resorting to physical violence is likely to lead to legal consequences and potentially serious trouble.
It's essential to deal with such situations calmly and responsibly. If you find yourself in a similar situation in the future, it's best to try to diffuse the situation peacefully or seek help from an authority figure, such as a store employee or security personnel, to handle the matter appropriately.
If you have already engaged in such an incident, it would be wise to consider apologizing to the person involved and seeking legal advice to understand the potential consequences you might face. Legal penalties for assault or battery can vary widely depending on your jurisdiction and the specific circumstances of the incident.