Action Man head is an unfortunate stage during growing back hair from being really short. 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 resembles that 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
Have you seen Dan lately, he's tired of being a skinhead and he's growing his hair back in, he's totally got actionmanhead.