the term used to describe a dumb or slow person either self inflicted or not, generally a person who has and or does smoke too much marijuanaon a regular basis.
stoned gentleman on a beenbag mindlessly playing playstation one........ You walk in and say "you sir are a drophead" and leave
A Diphead is created by pushing on an infant's soft spotcarefully enough not to kill it, but firmly enough to mentally handicap it. They are used as portable bowls for dip and salsas.