1. Party PicsEveryone claims to know this rule, but pics of people drinking and smoking at parties continue to get uploaded to Facebook and MySpace every day.
Why it's dumb: Since anyone can repost photos online as much as they want, even pics that are meant to be private have a way of coming back to haunt you. Employers and college recruiters often check social network profiles before they make decisions, so one incriminating pic can ruin your life. (Remember what happened to Michael Phelps?)
What to do about it: Well, for starters, don't do anything incriminating at a party. Especially when there's a camera around (and there's always a camera around). If you're not sure how to say no to illegal stuff and still have fun, here are some tips.
2. Flirty PicsThis includes everything from those half-naked "sexting" pics to anything R-rated that you wouldn't want your parents to see.
Why it's dumb: Even more than party pics, flirty pics tend to change hands and get reposted very quickly. You might think your pic is for your sweetie's eyes only, but once you send it, you lose all control over where it ends up. Jealous exes sometimes share, and proud boyfriends and girlfriends have been known to show off.
What to do about it: It's okay to be sexy. Just don't be sexy in front of a camera.
3. Your Phone Number or AddressSome social networks let you post contact info on your profiles, and some let you send public party invites where anyone can find your address.
Why it's dumb: Broadcasting personal info on a social site might be the easiest way to share with all your friends, but it's also the easiest way to share with creeps, weirdos and other strangers you don't want knocking on your door.
What to do about it: Only share that info in private messages and emails. It might take longer, but it's a lot easier than changing your number or screen name to keep a creeper from contacting you again. And instead of creating a party invite page, just send out emails through a site like Evite.
4. Complaints About Teachers and BossesSocial networks seem like great places to gripe about school and work, right?
Why it's dumb: Remember: whatever you write can always get back to the person you're writing about. If what you say is untrue, or even just unflattering, it could get you suspended or fired - like the one 16-year old girl who got fired after she told her Facebook friends that she thought her job was boring.
What to do about it: Save your kvetching for when you're with your friends in person. It's more fun that way anyway.
5. Your DramaSocial networks are hotbeds for friend fights, breakup fits and nasty rumors. With just a click of your mouse, it's super-easy to share the dark side of your social life.
Why it's dumb: Some conversations need to be kept private. Getting personal in public damages your rep, hurts friendships and creates even more drama.
What to do about it: Don't use social networks as a place to have it all out with your friends and enemies. Instead, use socnets to share positive stuff about yourself and the cool things going on in your life, and keep the private stuff private.