1. Politics.
You're always going to have that one aunt or uncle you're going to end up wanting to fight in the front yard. Save yourself the food and energy by just waiting until the next holiday. Maybe one where there isn't so much food. Anniversary dinner, perhaps?
2. What you're doing in school.
The answer's really a lot of this - except you're not only sleeping, you're also dragging yourself to class half asleep. It's probably better to let your parents think you're getting up to get to that 8AM economics class every Monday, Wednesday and Friday. You know. That one across campus.
3. Your social life on campus.
For one, this could prove to be a very big problem if you're underage. But also, there's a good chance that as soon as you mention packing your body into a sweaty frat house every Friday night, you're going to be in for a lecture or two from your most uptight family member.
4. People that aren't at the table.
Uh, first of all, rude . Second of all, there's probably something someone at the table knows about that person that they haven't told to the rest of the family - and once the family finds out, it was probably for good reason.
5. Past events/holidays.
This one's for your own good as well as everyone else's. Not only does not talking about the years past save you from potential embarrassment at the hands of your family, it saves them from trying to one-up each other with stories about whose child was cutest.
6. Potential significant others.
Look, just because they're single at the moment doesn't mean they play for the other team! Maybe it was a stressful time of year. Or maybe they're already plotting next year's fake significant other so they don't have to go through this again.
7. Your relatives' love lives.
Look, they're just tryna enjoy a gathering here. They'll get married/have kids when they get to it, okay? No rush, fam. And don't place any bets on them, either. That's just rude. (Behind their backs is another story, though.)
8. Parenting techniques.
Everyone parents a little differently, okay? It's not your business to tell someone else how to parents, even if you secretly disapprove of how they run things.
9. Finance.
This is a MUST DO NOT DO, especially if you've several different relatives that all work in finance or something to do with money. You'll end up with five different pieces of advice on what to do with that nickel you found on the sidewalk.
10. The next gathering.
Don't start planning the next one until you've finished this one. It just leads to arguments and details no one'll be ready for and will probably forget as soon as they leave.