Holy cow! That sounds terrifying. We've had a walk-in 20-25 top in the middle of a Saturday night rush, which definitely had potential to get a little hairy, but they were rather clear from the get go about how to split up the checks and everybody left happy. That just sounds like the GM nightmare.
FYI- any servers out there- the server dream may stop when you get promoted or get a different job, but the GM dream is just as bad, except servers are yelling at you in addition to guests
