Someone who is Sick (in the) Head.
Hence Sick Head.
This is a person who tends to do crazy dangerous and slightly harsh things. This involves getting in fights and going crazy.
(See Jack Brett)
I wouldn't start on that guy he is a sick head, and will put you on the floor
when a girl or guy gives you head while she is driving and you are in the passanger seat, and as they are going down on you, you call out the directions and when to stop and go
this girly gave me reverse road head, it was going fine till we crashed
A person (normally a girl) who has absolutely no sense whatsoever and has problems knowing whether or not they are a whore. The majority also tends to fail in school and the ones that don't are the rich ones who have sensible parents. Yam Heads come in all shapes and sizes and you are able to instantly know a yam head if she asks you where to locate the nearest stone. Some Yam heads have very bad whoring tendencies and often lead themselves to get fucked over by men but still find themselves running after fuckboys and still claim that all boys are assholes when they leave the good ones in the friendzone. :)