Man-Machine Interface

Man-Machine Interface is a challenge added in the Gun Runners' Arsenal DLC for Fallout: New Vegas.

Obtaining
To complete this challenge, you must kill 15 Mojave Wasteland Mr. Gutsys or Sentry Bots with brass knuckles, spiked knuckles, tire irons, or lead pipes. It can be one or the other, or a combination of both.

Behind the scenes
This challenge is most likely a reference to Masamune Shirow's Second Ghost In the Shell Manga series titled "Ghost in the Shell 2: Man-Machine Interface"