BASSA is right that we are under no obligation to mix with certain people downroute. It's our own free time and we can do whatever we like with anyone we like. BA cannot tell us as to whom we should and should not interact and socialise with on layovers.
Respecting the chain of command is another issue. The captain is the captain, yes. The first officer is the first officer, yes. Just because I prefer to be with somebody else downroute doesn't mean that I'm disrescepecting them or the chain of command.