To earn this achievement you need to roll a 1 or 20 on a Dice Chest.
Dice Chests are unique to areas located in Tiny Tina's Assault on Dragon Keep DLC. If you've yet to begin Tiny Tina's DLC it can be accessed by visiting Unassuming Docks at a fast travel station.
Dice Chests are easily recognizable, they simply look like a normal red loot chest, but with 2 colored 20-sided dice on top.
Eridium is required to open these chests, and the player can choose to spend 1E to roll one die, or 5E to roll both. (The only difference here is that the higher number you roll, the better the loot you get).
Earning this achievement is luck based, I made it through the whole DLC without getting it on my first playthrough.
Lower level solo friendly method:
*** Spoiler - click to reveal ***One location I recommend is using the chest in the Heart of Nightmares area (where you fight the second to last story-related boss) located in Lair of Infinite Agony. After defeating the boss there is a room in the back that opens up, inside there is a door to Dragon Keep at the back and a Dice Chest on the right. If you wish you can roll the chest and Save & Quit to respawn right back in front of the chest, (but you need to re-defeat the boss again).
If you don't want to fight all the way through Lair of Infinite Agony to the boss room, you could fast travel to Dragon Keep and just go backwards down the lift and take the back door into the boss room (but again you still need to defeat the boss to deactivate the shield on the chest).
Another, and probably better location, requires you to have the ability to defeat the raid boss dragons. On Normal Mode these are around level 38 for a solo level 50 character:
*** Spoiler - click to reveal ***Thank you to the comments for pointing this one out!
To get to the raid bosses you will have to first have beaten Tiny Tina's DLC (or join on someone that has). First fast travel to Lair of Infinite Agony, head right through the hallway, take the lift up on your left, you'll end up in a dead-end room with lots of spiders. On the right turn the knob on the wall and it'll open the door directly behind you that was closed previously. Jump down and head right and then take another right up some stairs, theres another knob to open the door in front of you into a room full of skeletons. Theres a statue directly in front of you with a bowl, you have to put 20 Eridium into to open the secret door. Jump down and enter The Winged Storm. Once there it's pretty straight forward, make your way towards the platform and activate the scroll on the large spike in the center.
There are 4 of these dragons you will have to defeat, but in doing so you will earn the "Make it Raaaaaid" achievement. For more help with fighting the dragons check out the achievement guide for that achievement:
After defeating the dragons a bridge will extend to the platform and the gate will open. Head straight through and head up some stairs. In this area there are 35+ dice chests for you to open!