Requirements:
1 - USB Flash Drive

How do:
1 - Get 1(or more) challenge 1 away from completion.
(Preferably a level 5 so you get 100 badass everytime you do this.)
2 - Save the game to your flash drive.
3 - Load up the game from your flash drive.
4 - Pull out flash drive and don't select a save device.
5 - Complete challenge and quit without saving.
6 - Repeat 3 - 5

- To re select your memory unit just go to options in the main menu and select
change storage device.

Your badass points are stored to your actual profile while the challenges are saved locally to your hdd/mu. So when the challenge completes it adds to your points but doesn't check which challenge was complete nor if it had been completed. You can do this with lower challenges like level 2/3/4 but it will not make your badass rank go up fast.

One love,
Shotty