Yellow Paper communication.

I found out that the pot in my loo had blocked and I had put 2 post-it(s) on the door of the bathroom saying "The flush does not work so please use the other loo". The sub-roomie of mine had to hurry that day and ran into the loo without reading the post-it and of course had the bathroom flooded. After he comes out he has this tone where he has made a mistake and we had this conversation

he - "The bathroom is not working I think there is some problem."
me - "I had put the post-it there didnt you read it?"
he - "Oh the yellow Paper??"

There ends the conversation. I was speechless. I for a moment feel that it is my fault as I should have woken him in the night to tell him that the loo will flood if u flush it. So much for my very formal way to communicate with him.