(UPDATE: I've added a new example, thanks to Sensorium for reminding me, and I've added comics! Everybody loves comics!)
Now I'll be the first to admit that I'm not perfect. I've screwed up many times in the past, and I'll screw up in the future. I fully expect that there will be times when a significant other will be upset with me, and that I'll either fully deserve or at least understand what's bothering her. And I'll probably apologize, and then we'll have make-up sex or something.
But sometimes, sometimes there can be no apology. How do you express regret for something that you never did? Consider the following:
The other day VigilanteGirl and I had a misunderstanding over a potential date. I thought she was blowing me off by not answering my invitation, and she thought I was being an asshole by not following up on her acceptance.
Like I said, it was a misunderstanding. A communication failure. I simply didn't get her message. Once I realized this, I stopped being irritated with her. Once she realized this, she for some reason decided to stay angry at me.
The Preemptive Pout
MixedSignalGirl was the queen of this. She'd imagine some time in the future when I'd anger her or make her sad, so to save time she'd just go ahead and get mad or sad right away. Asking a woman in this condition what's wrong will get you the standard "nothing" for an answer, but in this case it's actually true. There is nothing wrong, but there almost certainly will be at some point, so she's just beating the Christmas rush.
Probably my favorite. This is where a woman is allowed to punish a man for something he did wrong in a dream that she had. In my life, I've been punished for everything from calling a woman fat to murdering and eating her parents, and for everything in between. Apparently my dream-self is a real asshole. But does he have to pay for his misdeeds? No way. I have to pay for them. Over and over and over.
The Old Wound
This is when something you do reminds her of her last boyfriend, husband, or whatever. The only way to be sure to avoid this situation is to only get women by rescuing them from convents.
So, what's a guy to do when faced with these situations?
Easy. You've basically got a free pass. You're already being punished, so you may as well earn it. Go out drinking with the guys all night. Eat a shitload of White Castles right before bedtime. Flirt with her sister. Call her precious poodle a yapping rat-dog. Give her something real to be upset about. You'll feel better, and she'll feel justified.
And then you'll have something to apologize for, and then you can move on to the make-up sex.