Since the other thread (about who pays when friends go out to celebrate a friend's birthday) got locked, I'm starting this one to ask how this situation should have been handled.
The birthday boy's friend invited a bunch of the birthday boy's friends to a restaurant to celebrate. The friends came from 2 different circles. One circle was used to everyone paying their own way, and splitting the birthday boy's dinner. The other circle was used to everyone (minus the birthday boy) spliting the total bill. The difference between the circles was not noted until the check arrived and everyone threw down cash per their expectations. Since the second circle had ordered significantly more extravagantly, the cash came up quite a bit short.
It was the inviter's mistake not to state the conditions of payment upfront to all invitees. But once the deficit situation presented itself, how should it have been handled ? (I'm afraid to say it was handled badly by most - some from both circles defiantly or passive-agressively refused to pay more, others grudgingly paid more - although a few graciously paid more. Basically, a mess, and an unpleasant end to the celebration. After this, I never attended another of these.)