Here is the full list of all 12 Karen: An Outrage Simulator achievements.
True serenity, through the misery of others
Spoke with the manager, and destroyed him
Expiry dates are just suggestions
You are now Karen
Lose your cool at the Con-Mart
Throw a tantrum at the Starcups
Go ballistic at the spa
Nobody's having a good time if you aren't
Rage at the restaurant
Nobody tells you what to do
Erupt at the grocery store
You have reached the ultimate form