I saw my first one of these the other day. On SAS not BA. They seem to have far fewer rows of their euro business seat (called Plus) than BA do of CE.
One chap who looked a bit like a rugby player was sat in 3K. I noticed some sort of conversation with the cabin crew member. The passenger seemed to think they were right. Followed shortly afterwards with a very loud "Can I see your boarding pass please" followed by "33! K sir" said loudly enough that everyone at the front of the bus could clearly hear. He probably claimed it was a genuine mistake based on the numbers, but you could clearly tell by his body language that he had been trying it on and got caught.