I walked in on 2 different parties in my life in a hotel, and its a bit delicate.
ONce, in Atlantic city checking in at around 1am, I walked into a room, (ALWAYS put the chain or security lock on for this reason, so someone else cant walk in casually), and being the late hour, I was half asleep myself, I walked right in, was about to turn on the light, and there was an elderly couple sleeping, snoring loudly that caught my attention in the bed, I was glad they didnt awake to find me entering, I quickly exited, actually a bit shook up, and went to the front desk and gave the checkin girl a mouthful.
The second time, was last year, the Hamptons Inn Binghamton, NY, on the way to visit my kid up in the Buffalo area of NY, it also was very, very late, as I worked that day, and didnt leave NYC area till 8 pm.
I opened the door, and a man around 40 and his son were sitting directly opposite the door in their boxers speaking with someone I couldnt see, and they looked at me and were in shock, or at least they looked totally shocked.
I said sorry, turned my head down and walked right out. Before I got to the desk they had already called and complained.
I realized the dumb mistake I made by turning away from them as to not invade their privacy because at that moment who would know if the person would attack me as an intruder or whatever, it wasnt my fault, and I really laid it into the late night women behind the desk.
I made her go up to the next room and open the door first.
Its not a pleasant experience.
I got married while I was still a student, and I could not go on a honeymoon until I finished finals, so on my wedding night we made some last minute plans to stay at a hotel in Manhattan and catch the Beatlemania show on Broadway, the next day, then I had to get back to school on Monday.
At around 5:30 am, a bellhop attempted,(keys back then) to open our door, the chain stopped him and he yelled out Im sorry, wrong room.
I called the front desk ofcourse, just to make sure it was a bellhop, but didnt make a fuss over it, mistakes happen.