To Kill Demons...

In case the obvious escapes you, this is a series achievement which you earn in the following order:

1. We Came Here For Two Reasons Slay 100 non-trivial demons on Argus
2. To Kill Demons... Slay 500 non-trivial demons on Argus
3. ...And Chew Mana Buns Slay 2000 non-trivial demons on Argus - Reward: Mount [item=153041]
4. And We're All Out of Mana Buns Slay 5000 non-trivial demons on Argus - Reward: (Account) Title Demonslayer<Name>

Origin
While many believe the quote originated from the video game Duke Nukem 3D, it actually comes from the 1988 movie They Live. In the movie, a man named Nada, played by Roddy Piper, finds a pair of sunglasses which lets him see that aliens are disguised as humans, and discovers hidden subliminal messages everywhere. Nada then steals a police shotgun and whist evading the police stumbles into a bank proclaiming “I have come here to chew bubblegum and kick ass…and I’m all out of bubblegum.”

Derivatives
Abundant Internet meme use
Yugioh – Episode 11 “I’m here to kick ass and play card games and I’m all out of cards”
Yugioh – Episode 23 “I’m here to kick ass and drink cups of tea and I’m all out of tea”
IT Crowd – I came here to kick ass and drink milk and i’ve just finished my milk.
Dazed and Confused – I only came here to do two things, kick some ass and drink some beer. Looks like we’re almost outta beer.

A good place to farm for this is Darkfall Ridge in Krokuun (60.3, 78.7). It is located just below the Vindicaar. Talk to Grand Artificer Romuul at the navigation console to take you to the surface, then follow the path until you see the guards fighting. Constant stream of mobs from the two portals, with one elite, and guards to help kill. Bring friends, it goes faster.

Also, the title reward should've been "Rowdy", not "Demonslayer".