As the description of the achievement says:
Destroy an enemy’s weapon with a perfect guard
The Perfect Guard happens when you time your guard just right, parrying the enemies attack no matter what they throw at you. The Perfect Guard protects the player from any status effects. Furthermore, you won't consume as much stamina as a normal guard.
So simply time it right with any enemy to destroy their weapon, can be done with bosses also. early puppets with sword near Mad donkey and Watchman boss are recommended.
Timestamp: 01:31:55 (part 1 video)
Destroying the weapon of an enemy also reduces their damage overall.
100% Complete Walkthrough guide for all achievement/collectibles and Full Game.
All Timestamps are in YouTube pinned comment.