Australian saying. A boofhead is one who is a little slow, or maybe just does silly things. I'm a boofhead, thats why im writing this, it's silly. Generally good natured. The sort of person who drinks and gets so pissed they decide it's a good idea to shout people you barely know drinks.
Someone who smokes excessive amounts of marijuana using a bong. Usually these people hang around in groups of bongheads (often in a garage or a very unclean welfare house). The conversation in a house full of bongheads is usually about either mind numbing boring shit with no purpose or if they are intelligent bongheads the conversation will vary between aliens and star wars.