Your rarest steam achievement.

Waylaid from 100% Orange Juice - 0,22% have this.

I have the "There Is Only War" achievement for Space Hulk, which only 0.2% of people have. It's remarkably tedious and the only way I was able to get it was to create a macro to have it automatically do a bunch of things and have the game run overnight a few times.

Also I have a bunch of achievements for Civ 5 which only 0.2% of people have. It's easy to get the achievements for Civ 5 if you download the right save game files.

Mad Bomber (0.10% have it) from Tactical Intervention, I don't know even how I got it and why so little players have it.

Tactical Intervention

Makin' Bacon
Ignite 3 or more Counter-Terrorists with one Incendiary Grenade

0.37%

Europa Universalis IV
Basileus
As Byzantium, restore the Roman Empire.

1%.

Well, according to AStats:
Knowledge is Power (Sid Meier's Civilization V)
As Assyria, use a Royal Library filled with a Great Work to train a unit that begins with a promotion.
2.5%
Probably because I don't try to get achievements. :P

Goat Simulator - Hang tight (0.17%)

Winter Voices - The Shoreless 0.40%

I need to replay that game D:

0,39% Shatter: Buddies Forever. Made it together with my wife

Mine is "Small Arms Enthusiast" from War Inc., own only by 0.51% of the people. To be honest I'm not really proud of it, since the game sucks.

Dungeon of the Endless - I Could Quit If I Wanted To, 0.53% have it.
Not hard just very time consuming.

my rarest is Katagelasticism in rogue Legacy.. its the only game I 100% 'd :/

second rarest is a geneoid kill in galactic arms race test version(which is lol worthy seeing as I didnt play it very long)

Financial Storm (FM2014) - 0,18%

Brazilian Hero - Football Manager 2010 - 0.14%

All my other rarest are from Train Simulator DLCs that not many people bought.

My rarest 6:
Awesomenauts - Wrecking Wilson's Garden (0.28%)
Sid Meier's Civilization V - Silk Road (0.30%)
Sid Meier's Civilization V - Losing My Marbles (0.33%)
Sid Meier's Civilization V - Pillage, Then Burn (0.45%)
Sid Meier's Civilization V - Radio Free Europe (0.50%)
Sid Meier's Civilization V - Longest. Name. Ever. (0.55%)

Posted the top 6 merely out of the curiosity that 5 were from Civ 5, despite 1st being from Awesomenauts, lol.

"New york minute" in "No more room in hell". Only 0.07%. LIKE A BOSS!

Tom Clancy's Ghost Recon Phantoms - Recon Qualification V (0.70% of players have it), I'm actually close to completing this achievement for the other 2 classes as well (almost)

Goat Simulator - BFF 0.75%

Privet in I Shall Remain 0.35% got it
Hardcore Veteran in torchlight 2 0.36% ppl got it ;)

Skull Cracker from Killing Floor. 0,55% of players have this achievement.

Ace of Spades
"Feeling Flush" Achievement (0,07%)...

funny, because you can get this achievement very easy :D

Complete a campaign on Legendary in SHOGUN 2: Total War. My next target is to capture whole world as Ryuku in Europa Universalis IV

Hammerwatch: Combo Master (0.79% apparently :D)

0.99%
Unlocked Nov 7, 2014 @ 4:45pm
High Five
High five Duck in Long Road Ahead on The Walking Dead table.

Though i think some of these stats are not 100% because of SAM

As i have seen people shortly after the release get some rare and hard ones within a short time and with not even enough hours to beat the game.

And for that reason i do not put much stock into achievements i know they where meant to prove you did something in game,as before all you hard is your word but since they can be faked so easy,in the end it still back to weather you believe the person or not.

Though the one i posted it not really that hard to get,just a bit of time and a good run on the pinball machine,i think mine is so low because not a lot play it enough.

Mine is Rare Collector from Dishonored, 0.34%