Action Man head is an unfortunate stage during growing back hair from being reallyshort. Eg. After shaving of a Mohawk. The hair reaches a stage where it is longer than it was but still too short to do anything with. The result means the bearers head, closely resemblesthat of an action man doll, both in terms of look and feel.
Aw dude, I really regret shaving off my Mohawk, I've totally got action man head