You may really enjoy this article about the very phenomenon you're talking about. Very interesting. When it's the company card, rules are different. I will never get into a situation where I do equal splits with everyone at the table if there's hams present and paying for ourselves. Been on the losing end of that way too many times! http://www.slate.com/articles/life/a_fine_whine/2008/10/happy_birthday_you_bastard.html