Dating Commandment: Thou shalt honor thy dating commitments.
How They Broke It: Chuck and Blair were supposed to be on a couples vaca to Tuscany. But the notorious playboy surprised no one (except maybe Blair) when he left his best girl high and dry at the airport terminal so he could go slut it up with another woman. Come to think of it, what commandment hasn't he broken?

Dating Commandment: Thou shalt let the man take the lead and shalt avoid bringing personal baggage to the table.
How They Broke It: Pam had around 300 pounds of personal baggage. It was called Roy. Pam played pretend in love with Roy while flirting shamelessly with Jim for two seasons before the office prankster finally took the hint and made his move. But Pam refused to fall into Jim's arms and dump Roy, the dead weight. Because they broke a dating commandment, P&J's relationship took forever to take off.

Dating Commandment: Thou shalt not, under any circumstances, speak of any other romantic relationships.
How They Broke It: Hey "Friends" fans, remember the one where Rachel gets tanked, steals a cell phone, calls Ross, leaves a declaration of love on his answering machine, and does it all while on a date with another guy? The lesson: Don't tell your date that you're pining for someone else. You'll be the star of their worst date story.

Dating Commandment: Thou shalt not drink too much on the first date.
How They Broke It: Meredith drank about ten too many on her first date with Derek, if sleeping with a nameless stranger you met at a bar is a date. Of course one could argue that Meredith drinks too much, period. But with "dark and twisty" insides like hers, who wouldn't?

Dating Commandment: Thou shalt act like a lady.
How They Broke It: Kate is just another one of the guys on the island. She shoots! She spits! She swears! She has prisoner sex with Sawyer in an animal cage! ON TAPE! Kate better clean up her act. The dating commandments still apply to castaways on time-shifting islands. Really.

Dating Commandment: Thou shalt (if interested) express some interest.
How They Broke It: House is totally in love with Cuddy, and Cuddy is totally in love with House. Somebody needs to lock these two in a room and make fun of them till they kiss. They both respond favorably to insults and mockery. Sometimes it just takes that extra push.

Dating Commandment: Thou shalt not become intimate on the first date.
How They Broke It: You really can't blame Big for sleeping with Carrie on their first date. She showed up at his place wearing a dress that screamed sex, and the night was quickly relocated from a restaurant to Big's bed. They overcame the "sex on the first date curse," but their subsequent rocky relationship can trace its beginnings to their first date sleazefest.