"Not Full Of Monkeys" is a challenge that you meet by killing enemies with stationary barrels of any type. Well, with Gaige the Mechromancer DLC, you don't need the barrel! Anger a swarm of Rakks and summon the Deathtrap. They will rush you, and the Deathtrap will use it's laser to kill them. It counts as a stationary barrel this way. Try this on all flying enemies for some quick Badass rank!