Green’s Dictionary of Slang

a happy-go-lucky, eccentric person.

1969		N. Cohn Awopbop. (1970) 154: Charlie Watts played the all-time bombhead drummer, mouth open and jaw sagging, moronic beyond belief.
1977		A. Bleasdale No More Sitting on the Old School Bench (1979) 61: Look at them, yah, blue eyes, bomb heads.
2016		A. Wheatle Crongton Knights 235: I knocked a bombhead over once I gotr outside.