I once had a maid walk into my room at 7am in an InterContinental. The DND light was clearly on so there was no excuse. This property had no deadbolt (and still doesn't) so there's no way I could have prevented this from happening.

To make things worse, the maid turned on the lights in my suite. When she saw that I was still in bed (I was awoken by the sound of the door opening), she immediately turned around without saying a word and scampered out of the room, leaving the lights still on and the main door ajar. To this day this is one of the most bizarre things I've encountered in a hotel.