About 6-7 years ago, I was at the Westin ORD and had the DND sign on the door. Since I had room service there was still a tray in my room. It was a big room with the bed far from the door. About an hour or two after I ate, with the DND sign on the door, someone came to the door, knocked once and entered immediately, I jumped up and yelled, he slammed the door and ran out!! I ran out the door in shorts with no shirt on and he went down the stairs by my door, I yelled to him, he stopped and gave me his name and said he was coming for the tray. I called hotel security, the manager came up and apologized and gave me 10,000 points for the incident.
I still to this day think it was not just a tray issue and always put the bar on the door now.