How should I?
A) Prepare a magma 'SCREW THE WORLD!' device
B) Breach HFS
C) Catsplosion (FPS death)
D) Mass Dwarven Suicide Chamber
E) Burning lignite bins + Overworld Map
F) Give everyone a pet alligator.
G) Last Dwarf Standing super-survivor arena
H) Mass Artifact/Masterwork destruction
I) Cave the entire map down into the magma sea
J) Prepare a REAL goblin siege, with 100+ goblins, 20+ trolls, and various mounts unleashed behind my defenses and see how far my traps can go? (Armok's favorite, i'm sure.)
K) Variation of J. Goblin Supersiege vs. The Clown Aramada?
L) Get the worst noble possible (though selective magma-ing) and attempt to have all my dwarves jailed at once?
M) Forgotten Beast Blood Sauna?
N) Prepare a ginormous dwarf-launching bridge and fling everyone in random directions
O) Use Runesmith to blind all dwarves and see just how they fare
P) 'Bad King', specially isolate a very demanding Forgotten Beast Adamantine King to where dwarves can come 'serve' him but he cannot escape the fort
Q) The Dwarflander, drops dwarves from 3 z-levels with no medical intervention, allowing only those who survive to continue
R) Go Hippy, stop eating meat, using wood, metal, and farming and live off the land- and on the land
S) How I Make Babby, kill all female dwarves and let them age to death
T) Vomitorium, force every dwarf to cave adaptation then lock them in a bright, shiny room with food and booze for a lifetime and see how long they last (without beds)
U) Hazardous Workplace, put an automated upright spike (menacing spike) trap behind the door of every workshop and watch OSHA have a fit
V) Aquadwarves, dump them into 4/7 water labyrinth with a few breathing spots lined with traps and carp venemous water monsters, and see if anyone survives?
W) Yggdrasil, attempt to build a 50 z-story tree (out of wood, of course) and survive the elven hypocritical ambushes
X) Dead Weight, attempt to replace EVERYTHING possible with lead, and watch my dwarves crawl to a halt. Also, no booze.
Y) We're All Mad Here, use Runesmith to force all but one dwarf into a strange mood at once.
Z) D'oh, make everyone a miner and cause them all to die by digging into something unintelligent.
D FOR DWARF) Build a 'Dwarven Laboratory' and cage all manner of horrific beastiest, for !!SCIENCE!!. Nothing can possibly go wrong, unless that janitor accidentally pulls the 'off' switch on the 10 megaton ectoplasmic containment unit. (Bonus for Doom references)