"dead bored" is a correct and usable phrase in written English.
It is commonly used to emphasize how boring a situation or experience is. Example: I was so dead bored during my math lecture that I couldn't concentrate on anything the professor said.
Beginning at 75, I became much less good as a proofreader and I was less observant of small details because I was dead bored by it.
Don't write, "The only reason I'm writing a diary because I'm dead bored here stuck in the airport" or make sarcastic comments like, "Mom, dad, do you know the story of the people who read other people's diary?
Me and my old and new friend were meeting at the deepest level one can meet another human being, right there in the middle of a plastic coffee shop surrounded by tourists and drop-dead-bored waiters.
The snappers look at us, then look away again, dead-eyed, bored.
No sooner has our attention moved away from Constance than it has settled on Anne Montague, who slyly contradicts what we have just heard: "More often than not, the dead were frustrated or simply bored, and, in sinister vengeance, they often bored Anne Montague in turn".
She uses drugs, she sings, because she's "famous," because "she's bored," because "you're dead" (presumably Kurt Cobain), because she is "the worst and best dressed," and because she has certain unprintable problems.
The rest of the episode was equally as frustrating: Rickon Stark returned and is now a captive of Ramsay Bolton -- not to mention the young Stark's direwolf, Shaggydog, is now dead -- Tyrion was basically bored for a whole segment of the show, Tommen seemed to get brainwashed by the High Sparrow, and there was just a lot of political nonsense going on in King's Landing.
Clever, solitary and bored, she once bought a dead animal from the butcher and carried it home, for an operation on the kitchen table.
It seemed destined to rattle around an obscure corner of Instagram until its owner got bored of scouring Yahoo Images for dead sheep.
Nor have students always found much reason to head into a city that bored local teenagers derisively call "Mer-dead".
