I realize this is an old thread, but the interview dinner question is a unique part of the application process that a lot of people don't understand (and I didn't really either when I went through it).
The pre-interview dinner is a test. To successfully pass it, you need to do the following things:
1. Attend
2. Arrive on time
3. Wear business casual dress. Do not wear jeans, do not wear shortsleeves, do not wear a suit, do not wear a tie. Men, this means slacks with a button-up shirt with the top button left loose. No matter what they tell you, this is what you should wear, period.
4. Make small-talk with everybody in the room and smile. Don't keep to yourself, don't be boisterous and tell ridiculous stories. Don't ask too many questions. Don't be annoying.
5. Do not order alcohol. If you want to drink, you can do this when you get back to your hotel room. Alternatively, only if every single resident has ordered an alcoholic drink and most of the applicants have as well, you can have a maximum of one, either beer or wine, and drink it slowly. However, the lower risk strategy is to abstain completely. You do not want to be the guy who shows up 10 minutes late and immediately orders a beer only to realize that nobody else is drinking anything and that they are not paying for it requiring the bill to be split for you. This happened to me.
6. Order something modest from the menu.
7. Do not pull out your phone even once.
8. Do not leave early.
9. Do not go out afterwards.
Do these things and you'll pass the test. Think of the pre-interview dinner as a test and you'll be better off. If you're thinking of it as a fun social outing, which it certainly could be if you ignored all of the above, then you risk screwing it up. It's painful and something you have to get through. You can go out for real with your friends and relax when you get back home. Programs are different. Treat everything like a test and you won't risk screwing up your rank at the spot where the residents opinion actually matters. Programs can do ridiculously petty things when it comes to ranking. So-and-so wore too much make-up to the pre-interview dinner and was flirting with the waiter, lets leave her at the bottom for now.... it happens.