From Real Simple (a.k.a Real Obvious). I tweaked a few.
What Not to Say About Someone's Appearance
Don’t say: “You look tired.”
Why: It implies he doesn’t look good.
Instead say: “You look like Judy Garland on a thorazine bender."
Don’t say: “Wow, you’ve lost a ton of weight!”
Why: To a newly trim person, it might give the impression that she used to look unattractive.
Instead say: “Fifty down, 150 to go!”
Don’t say: “You look good for your age.”
Why: Anything with a caveat like this is rude. It's saying, "You look great―compared with other old people."
Instead say: “You look good for your age. Most people your age are already dead.”
Don’t say: “I could never wear that.”
Why: It can be misunderstood as a criticism. (“I could never wear that because it’s so ugly.”)
Instead say: “I could never wear that, but I would love to make a tablecloth out of the fabric."
What Not to Say in the Workplace
Don’t say: “That’s not my job.”
Why: If your superior asks you to do something, it is your job.
Instead say: "What does it pay?" or “I'm already on it. Go back to sleep."
Don’t say: “This might sound stupid, but…”
Why: Never undermine your ideas by prefacing your remarks with wishy-washy language.
Instead say: "This might sound stupid, so I figured you were the perfect guy to ask."
Don’t say: “I don’t have time to talk to you.”
Why: It’s plain rude, in person or on the phone.
Instead say: Nothing. When someone comes in, don't look up from your desk or computer, just point to the door.
What Not to Say During a Job Interview
Don’t say: “My current boss is horrendous.”
Why: It’s unprofessional. Your interviewer might wonder when you’d start bad-mouthing her. For all you know, she and your current boss are old pals.
Instead say: "My current boss is the Antichrist, born from the foul loins of a jackal, the son of Satan sent to earth to torment man and destroy everything that is good and pure. Not that there's anything wrong with that."
Don’t say: “Do you think I’d fit in here?”
Why: You’re the interviewee, not the interviewer.
Instead say: "Please don't let the fact that I loathe people keep you from hiring me for your customer service position."
Don’t say: “What are the hours like?” or “What’s the vacation policy?”
Why: You want to be seen as someone who focuses on getting the job done.
Instead say: “Can I take Friday off? I know you haven't hired me yet, but I wanted to go ahead and put in my request early."
What Not to Say About Pregnancy and Babies
Don’t say: “Are you pregnant?”
Why: You ask, she’s not, and you feel totally embarrassed for essentially pointing out that she’s overweight.
Instead say: “If that's a baby, I weep for your vagina."
Don’t say: “Do you plan on breast-feeding?”
Why: The issue can be controversial, and she may not want to discuss her decision publicly.
Instead say: "Do you plan on breast-feeding? I hope so. That would be such a waste if you didn't."
What Not to Say to a Single (or Newly Single) Person
Don’t say: “You were too good for him.”
Why: You are basically saying she has bad taste. And you’ll be embarrassed if they ever patch it up.
Instead say: “You were too goody-goody for him. He needs a nasty whore like me."
Don’t say: “I’m glad you got rid of him. I never liked him anyway.”
Why: She’ll wonder about your fake adoration for him while they were together.
Instead say: “Do you care if go out with him now?"
Don’t say: “How could someone as perfect as you still be single?”
Why: A statement like this comes off as a backhanded compliment. What she hears is “What’s wrong with you?”
Instead say: “What are you, a rug-muncher?"
What Not to Say During a Fight with Your Beloved
Don’t say: “You always” or “You never” or “You’re a [slob, jerk]” or “You’re wrong.”
Why: Speaking in absolutes like “you always” and “you’re wrong” is playing the blame game, and resorting to name calling makes your partner feel helpless, which puts him on the defensive and makes a bad fight worse.
Instead say: “Fuck you!"
Don’t say: “If you really loved me, you would...”
Why: The more you treat your partner as if he’ll never satisfy you, the less satisfied you’ll be. Controlling your partner by imploring him to do something isn’t a good way to build intimacy.
Instead say: “If you really loved me, you would shoot me."