It was me all along
When people borrow things it can really be annoying when they do not return them after they are finished. Like when your neighbor takes your lawnmower, cuts their grass, and keeps it for six months. Little things like that can really drive a person crazy, more than you would think originally.
It seems like this person was driven over the edge when someone took their x-acto knife and never brought it back. They posted a message for everyone else in the house to see and they got an answer. The person who used it was so sarcastic they wrote a new message with the knife.