Vampires steal holy relic to settle vampiric dispute.
The king was a doppelganger all along!

Crash on island overrun with Flesh-eating slime.
Wizard from future sad you don't remember him.

After the party is slain, adventurers wake up as their weapons. Intitially, their ONLY way to interact with the world is quietly wishpering into the weilder's mind.
Adventurers (medieval setting) find a CD disc with a real-life name of the RPG you are currently playing written on it. It's recongnized as something insanely magical. (Yep. My avatar.)
The world is menaced by eldritch abominations, party fights them. The wife of a party's leader is secretly a renegade eldirtch abomination.
Adventurers visit their сollective unconscious.
Adventurers find out that one of them writes lewd friendfics about them.
You thought you had identical twins in your party, but actually, one of them is a doppelgagner. They really trust each other and refuse to tell the party who is who. (oh hai doctor)
The party, as a whole, gains omnipotence. However, it can do things only if each member truly and completely agrees on what to do.
Adventurers fing enormious drug cache in the mayor's office in presence of some law enforcers. Mayor returns in a hour.
Adventurers are sentenced to death on occupied territory. Escape isn't a problem, but for each escapee, occupants execute ten random civillians.
Adventurers find out a true name of their hometown. It's from a bloodeldritch broodfester language.
Adventurers find out that in the town they are stayin' in, every person from 20 to 70 had intercourse with roughly every other person from 20 to 70.
The stars predict that one of the adventurers is a fated savior, but... you know for fact (yes, literally) that the stars are lying.
Adventurers find out that one of the Archangels and one of the Demon Lords are the same person.
A guy in a santa costume tries to assassinate one of the adventurers... wait. That was THE Santa Claus !
A male adventurer willingly and irreversibly swaps bodies with an ancient succubus. She grows cabbage and sells it on a marketplace. He gains wings and magical powers he never learned to use and a compulsion to seduce. every. male.
Adventurers save a mute, deaf orphan who communicates in a simple and reasonable way: descriptive geometry. (GM prepares a ruler, a compass, pencils, and lots of pre-drawn epures.)

Cool ideas, but they are all longer than eight words. Also, please separate them into separate paragraphs. I can't really read your post without getting disoriented.

On topic:
Everyone else in the tavern was murdered overnight.

Strangers say- "Call if you regain your memories"

Man, some things are hard to put into 8 words. Should we call the 8 word limit a done game and make a general plot hook thread?

Took the fall for parallel world doppleganger.

King wants divorce. Seduce the queen.

King wants divorce. Framed for adultery.

Bandits cornered in bank vault. Flush them out.

Accidental planeshift into a pocket dimension.

King demands you take a census.
(historically medieval and pre-medieval people hated censuses)

Compile a tour guide for fellow pilgrims.

Warring dimensions fight to become reality. Losers vanish.

Everybody has a monster. Killing it grants immortality.

Prophecy unavoidable. Fulfill it in least damaging way.

Campaign/book idea: charachters on a grand quest fight bosses symbolically representative of their own flaws, and getting legendary loot symbolizing their virtues. In the end, charachters realize they can't complete their initial goal, because of their flaws. Charachters get flung into the deep past, without loot. There, they discover spell that splits people into their best and worst halves. Worst halves defeat the best halves, trap them into weapons, using them as phylacteries, over the years forget about their origin, and evolve into those bosses, instinctively drawn to their young selves. When the young selves are drawn into past, weapons release their prisoners - their flawless versions, ready to end the quest.

Throw cultists bachelor party, discover their forgotten patron.

Evil monk is one day of fasting from apotheosis.