Where/How to obtain the criteria for the "Under Pressure" challenge at the Arid Nexus - Boneyard. Simply hit the button, and kill everything (all the Hyperion bots, that is) that comes at you.
Disclaimer: Borderlands 2 is a game developed by Gearbox Software, and published by 2K Games - I do not have any affiliation/association with Gearbox or 2K, nor do I claim to have any affiliation/association with them. I do not own, or claim to own, any part of the displayed content - this video is for entertainment purposes only.