What Happened Here?

I'm confident in my theory that when I go out of town some stranger enters my apartment and has a party without my permission. Now we all know this is an impossibility since I live alone and only I have the keys. (Who would want to put on a clandestine affair in my apartment anyhow?) But it has to be. I couldn't have left my apartment like this when I left town. Could I have? I would never leave a mess like this for myself.