Often used to enchance harsh assessments of the character of others.
Robbo: "That bloke? He looks like a deadset fuckwit to me".
That guys a dead set fucken poof.
Robert: Yesterday I totally flipped out and killed 100 pirates with my boner, and then wailed fucking HARD.
Some Idiot: Dead set!? WOW I AM PUMPED UP!!
Taken from the British TV drama Deadset, in which the cast find themselves alone in the middle of a post-apocolyptic wasteland dressed in drag and not nearly crunk enough.
"Didn't stop you from projectile vomiting and stealing a TV though did it?"