'We (Chinese) found this flag on the moon and think it might be yours (American). We brought it back in case you still want it.'
--Then we hand the Americans their
flag carefully wrapped and cased.

I am pretty sure the astronauts we sent to moon are educated adults, people. They are not going to act like kids knocking over other kids' sand castle, so please quite trying to think like a kid.

'BTW, Would you like to see a picture where we planted our Chinese flag? Its where you left yours.'