That's pretty messed up, on both sides.
Hardly.
Group of people come in, disrupt operational schedule (airports aren't exactly a place where you can just blow some time, delays are serious business!) AND then one of those people with questionable behavioural standards starts exposing himself, on an airline with according to the article distinctively family clients, meaning children.
The dude is probably lucky the manager got to him before a very protective parent did.
If he thought it was a great joke, then I have no doubt paying for a return ticket and flying with different airlines from then on is something he readily accepted for his little "giggle", which however is a thing that didn't seem to be the case as his friends had to pay for his return ticket. In which case he was simply incredibly stupid.