"I love your body... it looks like a swimmer's!"
You probably mean, "Your body is toned and athletic." She definitely heard, "Nice can, Ivan Drago." Basically, there is no place for the word "like" in a compliment, so stick to adjectives, don't get too creative with the metaphors and you'll save yourself from shoulder freeze.
"Yeah, my ex really liked Metallica, too."
If you learn nothing else from the words on this page, avoid comparing her to any other woman, pretty much ever, at all costs. Whether it's that she looks like Halle Berry (bullshit), reminds you of your mom (creepy) or is as cool as your best female friend (hates her), being compared to another woman, no matter how positively, leaves too much (read: any) room for misinterpretation.
"You ate that whole thing?!"
Sure, she weighs 100 pounds and you blurted this out in a moment of genuine awe, but there is no scenario in which it'll be well received. Comments about what you're eating are annoying in general, so you should especially refrain from making them about her, including, "That's all you're going to eat?" Yep. Shut up.
"Is that all you're wearing?"
The double standard works like this: she makes fun of your Slipknot t-shirt, you tell her how hot she looks even if she's wearing a grain sack. Offering a woman any other fashion advice is asking for blood. In this case, it also makes you seem controlling. If she wants to wear a dress that's more risqué than usual, get over your boner guilt and enjoy the view.
"You're right, Heather did look hot tonight."
She won't freak out right away. But the instant you make a positive comment about the physical appearance of her friend, that thought will be double-encrypted on her hard drive forever. Feel free to tell her that her friends are cool or funny or nice—that can actually score you points. Just avoid any references to her best friend's phenomenal rack even if it is, in fact, phenomenal. [pagebreak]
"Honey, 'irregardless' isn't a word."
We're all responsible for occasionally finger-banging the English language, but when you point it out in public, especially around others, you slap a fat social dunce cap on your girlfriend. The consequences will come in three waves: first, she'll be embarrassed and suddenly quiet; next, she'll stew for the rest of the evening, effectively destroying the mood at your gathering; third, your ears will spontaneously start hemorrhaging the moment you get home. By all means, poke good-natured fun at her privately, but if you correct her in public, tell your god to ready for blood.
Flash: women sometimes overreact to stuff. But when something's upsetting her, telling a woman to calm down comes off as dismissive. Want to make things really interesting? Tell her this while you're already fighting. The surest way to ensure she never calms down is to tell her to calm down.
"Do you really need another pair of shoes?"
You think you're being a voice of reason, but the way she sees it, she makes her own money and she can spend it how she wants. If she's awful at managing her finances, and you're worried that your apartment will soon be overrun with leather pumps and strappy sandals, you're probably better off telling her they make her feet look fat.
"We can turn the lights off if you want."
It might seem chivalrous in the moment—she's being coy, you're worried that she's uncomfortable—but don't say it, just do it. She won't think anything of you simply dimming the lights, but if you start providing play-by-play coverage, especially when she's exposed, she'll feel like the under-construction wing of the museum. In this case, words speak louder than actions.
"You're a c---."
In fact, stay away from all four-letter "C" words, including cute, just to be safe. And if she ever does something so atrocious that it warrants the C-bomb, you should say it as you're slamming the door on her.