Hey Chris,

although the whole thing seems idiotic take it serious about how you deal and react with it. It can easily be part of someone's strategy to get you out of the building and could be part of some background or documentation effort in a build up to evict. I have seen it before so be real careful. I'd send a formal response in a mail stating that no one in your appartment has done that and also cite your comments on hating watermelon in the first place.

-W.