Those are some good ideas. I guess I could come up with a few. Though I'm horrid at names.
* Insert lame mine pun here*: Kill X amount of people with a single mine.
Something about Stealth: Kill 5 people in a row without taking damage using a silenced weapon.
Bond move: Kill multiple people with a prop (probably the explosive barrels in Facility Backzone).
Mine achievement: "Watch your step" or "Detonator" or "Demoman"
Stealth achievement: "Silenced but deadly" or "Non-smoking gun"
Explosive barrel achievement: "Do you know where you are?" or "Know your battleground" or "I wasn't aiming for you!"
And here are a few I've come up with just now:
Ghostly-Kill 20 people with the Phantom
Just like the Old West-Kill 30 people with the Revolver
Iron Chef-Kill 10 people with the Hunting Knife
In the hole/Hole-in-one/Died in grave/Not afraid of heights-Die by falling off the catwalks on Cradle and into the pit at the bottom, the actual pit, not any of the other parts of the ground!
Die another day...and again...and again-Press F8 twice after being killed by anything else than suicide.