Please tell me, could i get brain damage from being hit by a plastic coat hanger?

Not likely: Traumatic Brain Injury(TBI) is caused by external force -- such as a blow to the head,causes the brain to move inside the skull or damages the skull. This in turn damages the brain. The adult skull is quite hard. Most plastic hangers without extreme deliberate force would not cause brain damage. Signs of brain injury such as confusion, nausea vomiting and sometimes headache. See Dr. if symptoms.