These are unlockables in Borderlands for the Xbox 360 that you'll get as you kill different types and numbers of mobs throughout the game:
When you kill a mob just by stomping it's head out, you'll earn "My Brother is an Italian Plumber" - homage to Mario and Luigi I assume...
Here's a fun one to earn, whack 25 different mobs by running over them with any type of vehicle, and you'll get "Get A Little Blood On The Tires!".
When you take out 25 mobs with some type of corrosive weapon, you'll earn the unlock "Facemelter"... wow, what could be better than that title?
Of course, if you take out 25 mobs with any type of shock weapon, you'll get the "1.21 Gigawatts" unlock... hmmm, where's Marty McFly when you need him?
What firebug won't love this unlockable? Take out 25 mobs with any type of fire weapon, and you'll get the "Pyro" unlock.
Take out 25 mobs with any type of exploding weapon, and you'll get "Master Exploder".

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Sirens, kill a mob with your action skill and you'll get "Truly Outrageous".
Hunters, kill 15 different mobs with your action skill and you'll earn "Careful, He Bites".
Soldiers, kill 15 different mobs with your action skill and you'll get the unlock "Down in Front!".
Beserkers, kill 15 mobs with your fun action skill and you will then unlock "Reckless Abandon".