I officiated a game last week, where, one team are less well known, from east coast, and the other a huge worldwide name from the west.....30 seconds in, I ignored a handball appeal against the "bigger" team and the other team captain who was in close vicinity came out with "right guys as predicted we are up against it here", as a rallying call to their teammates about what I took as a premeditated attack that as referee I would favour their more illustrious opponents. The ball rolled out for a goal kick, and knowing the captain was yards away I firmly and politely said "right, that's enough of that , cut that out nonsense straight away". No threats as to future sanctions, no finger pointing, just a clear response that I had taken on board the comments.
Player held hand up, "sorry ref". Not a single bit of bother for the entire game. I feel stamping out that mentality as soon as it rears its head is the best cure.