I thought of an arena nickname for players that use the unique knives in the game. For players who kill an enemy using the Butcher's Cleaver or "Old Chopper's" weapon, the Kukri, they could get the achievement "Chop Notch." [As in, "Top Notch."]
Maybe you'd have to kill most enemies using that weapon, or take down an enemy from full health with one swipe.
[If you take down an enemy from full health from stealth with one of these weapons, perhaps you could earn the arena nickname "Dark Slasher."]
