It’s one thing to admit to your friend that you were unfaithful, but it’s another to completely brag about it to all of your friends. That’s just wrong on so many levels. Not only that but there was a group of them that thought it would be funny to brag about cheating with one another, almost in a competitive sort of way.
Hopefully, the person on that train caught a name or two of their girlfriends, so they could somehow find them on social media and tell them about their unfaithful partners. It’s grim, to say the least. Karma will eventually get them. Next time, their partners might be sitting right behind them while they’re talking about their infidelity (via Traveler Dreams).