I had an interesting experience on a CX 777 flight from HKG to LHR earlier this year. Out of habit, I chose a D seat, I think it was 20 or 21, and was busy extracting my laptop and other assorted peripherals to get settled in for the flight, when an older lady started speaking Cantonese to me from the G seat. I quickly responded I didn't understand her, so she said asked me in broken English if I minded swapping seats with her son. I still remember her exact words, which were "My son, sit behind, you swap with him?" as she pointed to the seat directly behind me. So, I pointed to the seat behind me in response, which was currently empty and said "this seat right here?" and she said "yes" so i naturally agreed, picked up all my things and moved them to the seat behind. About 5 mins later, she spots her son was had just boarded, and waves him into my old seat.
I had received my welcome drink and was getting comfortable when a guy stopped next to me and told me I was in his seat. I looked up surprised, and he showed me his boarding pass. Naturally, I just assumed that the son must have been sitting further back, so I quickly explained myself, and leaned forward to ask to see the son's boarding pass so I could sit in his seat. As I am sure everyone who is reading this will have easily figured out by now, his seat was in 60 something in Y. So, I told the son that he had better get his things and go and sit in his allocated seat while at the same time apologising to the man I was holding up. However, his mother started yelling at me, and I mean yelling, saying god knows what in Cantonese, and yelling "you agree!, you agree!" to me over and over again. One of the FA's came racing over, so I explained the situation to her while the mother kept interrupting what I was saying to speak quite indignantly to the FA and doing the best DYKWIA impersonation I have ever seen. I actually give credit to the son, who sat there the whole time not batting an eyelid, perfectly expecting that his mother would get her way. Luckily the guy who actually owned the seat I was in was very patient and even had a chuckle with me while the whole situation was getting sorted out.
Finally, the CSM came and basically told the son in no uncertain terms to get up and move to his allocated seat. I went to start moving my things back to my original seat, but the guy still standing in the aisle offered to take my seat so I wouldn't have to move again. I think he just wanted to sit down, and luckily the J layout allows you to easily ignore the person next to you. I still find it hilarious that this lady clearly thought it was acceptable for me to take her son's Y seat!
On a more positive note, I found myself chatting to a girl in the gate screening queue at SIN before a flight to LHR on BA. She was gorgeous so I was happy to wait in the queue next to her chatting away and we continued the conversation in the gate area. I was in J, so when it came time to board, I asked her seat number and said I would come past and say hi during the flight. Soon after takeoff, I asked the CSM if I could swap my seat with a passenger in Y because I wanted to sit next to a friend. The CSM was a little confused with my request, first thinking I said I wanted to bring a friend up to the J cabin, so I repeated myself, and he said that would be fine. So, I ventured back into the Y cabin and asked the man sitting next to her if he wanted to swap with my seat in J. He looked up at me a little confused, so I told him I wanted to sit next to my friend so he could have my seat if he wanted. He asked me again, "so you are sitting in business class" and I replied that i was, so he didn't need to be asked three times! It was the best long haul flight I've ever had