It's about inappropriate behaviour. Different 'levels' obviously, but still inappropriate behaviour that could cast a bad light on the club.
Whatever the behaviour, it seems likely that they were all just irresponsible idiots getting themselves into easily avoidable situations. The club (Pep) quite rightly dealt with Foden and Grealish quickly - The fact that it was not kept in-house suggests that a very dim view has been taken over the event. The Mendy situation, like that with Adam Johnson, will be dealt with by the courts and the club will take appropriate action following the outcome.
Your reference to Joey Barton (another cretin) etc, is no more than a pathetic attempt to make yourself look clever. I would have expected better from you.