A Wedgehead is a member of the British Army's Royal Engineers. The expression dates back to when the Royal Artillery ran away in Crimea forcing the Engineers to rescue their guns before the Russians stole them. In the chaos, they used dead infantry officers' bodies to wedge the wheels to stop the cannons rolling downhill.
See that Wedgehead over there? He is thick as mince and a complete waste of rations.
Commonly used as an insult, someone with a fadgehead has a women's vagina on their forehead, usually slightly off-centre. Where it has been derived from is unclear.
A derogatory nickname for the Bitcoin worshipping cult known as the Corpus from the game Warframe.
It is derived from the fact that the helmets of normal corpus enemies look as if they've just stuck a refrigerator on their head.