FWIW
Flew Lufthansa Beijing->Frankfurt in First earlier this year. About 1 hour into the flight I noticed a chap in the cabin who hadn't been there previously. Turns out he was a close friend of one of the CC. Kept himself quiet though and spent most of the time in the galley area chatting with the CC.
More unusual was a chap sitting across from us. Had the meal and then perhaps 4 hours into the flight his wife and young child appear upstairs too. They sit, chat and again keep themselves to themselves. Enjoying the service.
Chap then goes downstairs (to biz?) with child and his wife remains upstairs and proceeds to get the later in-flight meal service. Afterwards she goes downstairs leaving the seat vacant. Finally he reappears in time for landing. I guess it's one way of both of them getting the first class treatment but only paying for 1 first + 1 biz fare!
The outbound flight was much quieter. Just me + wifey with the whole of the cabin to ourselves with 3 CC.
