--a cyclist that does not wear a helmet. The bonehead
part of the cyclist refers to:
a) the condition the cyclist will achieved if he/she were to crash and hit his/her head on the road, tearing up some valuable tissue and exposing bone from the skull
b) the fact that the cyclist has nothing in their cranium
c) the use of bone
to protect the head instead of a helmet;
d) behaviour on a bicycle that exudes idiocy.