This achievement requires you to melee 50 mines. The mines are the floating spiked balls that have timers on them. The mines will attempt to home in on your character, so I found if I waited to about a half second before they hit me and swung with RB, they would get swatted away and explode.
If you are looking for a good place to grind this, there are a couple checkpoints that would work. I found that the first checkpoint in Hell, right after using TrafficKing to unlock a couple doors, works nicely.
You will get about 9 or so mines that you can swat for this achievement. Even if you die, they count. So I kept swatting until the mines we're done, and then I would kill myself in the electric field in the same room. Rinse and repeat.
Also, of note, this achievement as well as the other cumulative ones will track over multiple playthroughs, so you can easily check the progress in the achievement tracker.