This is another situation of a food thief. Somebody was taking items from this office refrigerator. We see three passive-aggressive notes about separate incidents. But they didn’t expect the robber to raise the stakes to the next level by responding.
This is one of the most audacious reactions we’ve ever seen but we respect them for it. However, they may have made a fatal error by writing the note with a pen. If somebody recognizes their handwriting there could be a lot of drama. Perhaps they should have typed the letter, but they couldn’t resist (via Little Things).