Here is the full list of all 26 My Pet Rock achievements.
Beat the Game Using Elitist
Beat the Game Using Eye for an Eye
This isn't really a rock anymore!
Unlocked the Lawyer!
Beat the Game Using Russian Roulette
Or is it...?
Cool Name!
Killed 10000 Enemies
Unlocked the Scientist!
Killed 50 Bosses
Unlocked the Farmer!
Unlocked the Miner!
Fully upgraded the rock
Killed 25 Bosses
Unlocked the Janitor!
Killed 100 Enemies using fire
Killed 1000 Enemies
Unlocked the Task Force!
Killed 10 Bosses
Unlocked the Engineer!
Killed 500 Enemies
Unlocked the Citizen!
Beat the Game using WMD
Beat the Game Using Survival Mode
Surely you're still learning to play right?
Won a Prize from the Slot Machine 25 Times