Many years ago I worked for a large company with a lot of people coming and going all the time.
The office was a bit of a rabbit warren, so it was often very difficult to know where everyone was.
One day this young man came in, sat down and started working like there was nothing out of the ordinary. Most people in the office hardly gave him a second look. Eventually after a week had gone by, someone plucked up the courage and asked him who he was.
The reply was that he was "working for Ed". Ed was a rather amiable co-worker who, it turns out, had taken pity on this young student and offered him work experience without clearing it with the bosses.
I also knew a man who travelled quite a bit internationally. Whenever he had a layover of a few hours in Singapore or somewhere like that, he would go to the most luxurious hotel he could find. Once there, he would not check in, but stride confidently up to the pool deck, grab a towel and spend the hours sunning himself. No one ever asked him if he was a guest.