Fraudulent pax onboard AF/KL - your stories

I had a first time story last week on my flight ORD-CDG. I was in J at the window and I boarded first before anyone else to have the opportunity to take pictures of the new cabins while the flight was empty. At one point during the boarding process, a guy arrived and was obviously seated close to me and he started to install himself at this seat. The guy never said a word, so clearly he was not bothering me. But, my gut feeling was telling me that this guy was not a J regular. But of course nothing wrong with that. Every J regular had his/her first time and it could also have been an op-up.
He took the menu and amenity kits distributed, put the socks and slippers on. He had the Champagne pre-take off. We took off and minutes after the crew was released from their seats, one flight attendant came and ask him his BP. And then said, sorry sir you are in 40K (random seat number here of course). So they ask him very politely and with a lot of professionalism to leave and go to his assigned seat. He never said a word. But he took his time to take all is belongings.
The chief purser came to discuss with me afterwards and said that was a 1st time for her on a US route. She said that they have very frequently this problem on some routes and one famous for that was BEY.

I thought it would be funny to start a thread on this and share our AF/KL stories :)