Fighting Vipers

As requested I made a video to show how it's done.

I had trouble doing it by moving the stick right, left, right and left again (+LT). So I decided to wiggle the stick around and hit LT while going left. It worked after two tries and now I can do it every time. It is a fool proof way to get the achievement if the other solutions don't work for you.

The explanation to this achievement will be broken down to the lowest level for clarity.

Although the instructions to pull off this achievement are right on the description, it is a virtual finger twister to pull this off on a controller. Especially since the P+K+D button is mapped to LT by default. There are two ways to simply the issue.

Go into Control Display from the options menu and you should see the default arcade setup for a controller. Scroll down to highlight an individual button to reassign its purpose.

If you want to continue to use the controller as a controller, reassign the P+K+D button configuration to the Right Bumper. If you want to plan to use the controller like a makeshift arcade stick, map the P+K+D button to the Y button.

When your character is facing to the right, the player must rapidly move the left control stick right and left. (Think as fast as any QuickTime event in another game.) Make your controller click like a maraca because they’re moving so fast. Also notice how the final command is Left+P+K+D, which means Left AND the assigned P+K+D button at the same time.

So from a standing position and facing right, the motion will be RIGHT-LEFT-RIGHT AND (LEFT AND Y/RB AT THE SAME TIME.)

You will know when this is done correctly when your character’s armor clothing literally explodes off their body. The achievement will unlock moments after a successful unequip.

I found a very easy way to get this achievement. If you have a Rapid Fire Controller, simply set RIGHT to Rapid Fire.When game starts, quickly press LEFT twice and LT, this achievement will be yours. Enjoy.

You have to quickly input ->,<-,->,<-+P+K+D as the info says.

That is Right > Left > Right > Left + P + K + D.
As Ryot Control says, you can edit the controls to make it as simple as one button press.

What many guides aren't saying is that you can do this AT ANY TIME DURING A FIGHT, not just at the very start as you load in.
I also tried for a good 30-60 minutes with the D-Pad with no luck, switched to the joystick and did it second time. Where I was going wrong was in trying to do it at the start of the fight, if I failed I was exiting out and starting again. Don't. Simply keep trying it even after contact has been made in the fight.