Revenge is best served cold
Coffee cream is a privilege not all offices carry, and if you want to enjoy coffee with cream in the morning, you have to bring your own creamer. This woman was sick and tired of the person drinking her coffee cream all week, and she decided that simply talking to them about it wasn’t enough – she wanted to get her revenge.
Of course, we don’t know for a fact if she really changed the coffee cream with her breast milk, but it doesn’t really matter – the person who has been using her coffee cream should only think he was drinking her breast milk, and this thought it enough to teach him the lesson. He wouldn’t take any chances with her beverages from now on.