To unlock this achievement you need to shoot some Hot Butter on the floor in front of one of the Therizinosaurus, causing it to trip up. The Therizinosaurus are one of the dinosaurs that you encounter in Act 2 and they are the blue ones.
The Hot Butter Spreader is one of the upgrades that you can buy for the Flamethrower, so you will first need to find this. You can find one in Act 2. Then go to a merchant and buy the Hot Butter Spreader upgrade and the next time you encounter a Therizinosaurus, just shoot the ground in front of it and lure it towards you and it will walk over the Hot Butter and slip to the floor, unlocking the achievement.