Nasty!G 15

You can unlock this achievement early in the game by heading to the fossil fuel station located on the west end of Fairmeadows Ranch. Look for the distinctive yellow dinosaur mascot on the building's roof, spouting gasoline like a fountain.

Once you're there, you can get your goat onto the roof using the yellow lift behind the building as a springboard. Once on the roof, stand on the circular platform beneath the mascot's legs and interact with it, either by licking or headbutting. This will result in your goat being showered with crude oil from the dinosaur's backside, unlocking the "Nasty" achievement.