Was that a one time event or did it happen often?
That was the only time I had been on a plane where so many things happened. The aft lav door kept locking. About 2 different times, I had a passenger come to me and say, "Is someone in that bathroom? I've been waiting for 15 minutes... and I'd go back there, knock and check the door and open it, to find it empty.
It all started with the coffee pots in the aft galley. We had gone out to do the beverage service and replaced the coffee pots on the burners, then we went out to pick up. When we got back to the galley, every single coffee pot had flags on the handles. Some had two or three flags. (We would "flag" the pots to tell the difference between regular and decaf... and since it was my galley, I knew I had only flagged the decaf.) So the other FA came out and looked at me like I was crazy, and asked why I had double-flagged all the pots. I was like, "What are you talking about?" She goes, "I can't tell the regular from the decaf..." and showed me that all the pots had flags on them. I looked back at her and said, "Are you screwing with me?" She goes, "No! Are you screwing with me?" And that was how it started.
There were other little things going on... stuff being misplaced and misplaced again... things that didn't really catch your attention or could be explained away. But having six coffee pots with flags all over the handles was really something that made you go... WTH is going on here?
Now the cart coming out of the housing... that could have been explained away, but it was so weird... and something I never saw again. We had a hard landing, and the cart, which was back by our jumpseat, jumped out of the housing, turned itself, and went zooming up the aisle and slammed right into the cockpit door. We both sat there with our mouths agape. It did not touch anything on the way up... have you ever seen a cart move up one of those aisles that did not catch on an armrest or something else along the way? But again... it was not impossible, it was just super-unusual. And the fact that the thing turned itself 90 degrees and headed down the aisle was simply jaw-dropping. Plus, it scared the crap out of the pilots, which was a bonus.
Now I have lots of stories about spooky things happening in hotels, but that was the only time something like that happened on a plane.