You happen to suspect the other driver involved is drunk or has taken drugs then you should call the Gardaí. If someone is hurt, or there is substantial damage to the car, call the Guards (legally this must be done within 24hrs). You sense that the injuries require medical attention then call an ambulance immediately. The Gardaí will also be informed. In the meantime don’t move anyone with a suspected head or spinal injury.
You should call the Guards if you suspect that the car accident was caused deliberately. If no one is hurt and the damage is only minor, then it may only be necessary to exchange contact details and insurance information with the other involved parties.