Here is the true defintion.
The most important fact about a metal head is a person who is dedicated to the music. Not just classic metal or thrash or death metal. Nu Metal is metal to. I listen to all kinds of music death metal, thrash metal, and even Nu Metal. You people who are saying that Korn or Limp Bizkit are not true metal bands are not true metal heads so much as closed minded people who are afraid of change.
Another important part of being a metal head is you have to be a loner and only hang out with other metal heads. They can often be aggressive from being isolated from the rest of the world. However, they're very friendly towards fellow metal heads. They are not always likely to win in a fight like some have said. Many are wimps from sitting inside and listening to music or playing their instruments all day.
Many metal heads have longer hair but it's not a necessity. Leather is also not necissary and I prefer to not have it. Some heads wear clothes that are a little darker (not goth but similar) but again, it's not necisarry.
Gestures include swinghead back and forth with the rhythm of music which has been mentioned. But you guys forgot one important gesture. Devils horns. Index finger
and pinky extended into the air.
Metal heads also have to be rebels. They do whatever they want whenever they want but they are not always lawless. They are much less likely to kill people than a rapper.