Drunk on power Achievement
Drunk on power50
Upgraded all weapons to max
This requires you to purchase all the upgrades for the three available melee weapons and the four available ranged weapons. To unlock the skills for purchase, you must kill enemies with the weapon. I found several good farming spots throughout the game to keep upgrading/reloading. The part where you visit the 3 Deadpoolios on the "Death, Baby" stage and the door breach section during the "Road to Victor" stage are some examples. The door breach section is also a great section to keep reloading to get your ranged weapon kills to unlock the skills for purchase. Just make sure you buy a skill before reloading so it saves your kills/DP points.
Here's a video from deathmule showing a method of farming DP points near the beginning of the game: