If that is a real note, and someone actually left that on the door for you, sorry to say it is none of that person's damn business. If you have a relationship and it is making you laugh, more power to you!
I mean, very very generic and broad as to the circumstances and meaning of the note itself or why the person is laughing so much. However, why would someone write that? Just seems like they're overstepping for no reason or they're annoyed but trying to put it politely.