What types of story plots really piss you off?
For example, when the hoary old plot twist "It was just a dream!" occurs, people react differently - some like it, some feel cheated. (The "It Was Just A Dream" plot CAN be used well, for instance in many of Philip K. Dick's stories and novels. But it can easily be abused.)
It's a very common misconception that the writer "gives away his soul" in the characters he writes, while the plot is just a framework on which to hang the characters.
I think it's the other way around: the plot gives away the real message between the lines, and the characters are of secondary importance. We tell stories not to admire the imaginary persons' personalities, but what they do and why they do it.
If you see it that way, certain plots become too disgusting to stomach, because they clash with your convictions. I can forgive flaws in the story's characters, but I can't forgive plots with flawed messages.
Here are some examples:
1. "Saddam Hussein Writes The Plot" plots:
Saddam Hussein wrote a novel (I kid you not) about a warmongering usurping tyrant whose actions and policies were justified. Any story where the protagonist is a warmongering usurper/tyrant/emperor but it's always justified as "Good For The Country" or "Part Of History's Great Plan" makes me cringe.
2. "Horny Old Man" Plots:
A middle-aged man (usually a white middle-class type) goes to bed with a much, MUCH younger person... and the plot creaks and strains to make this seem extraordinarily Noble and Romantic and Rebellious...
...but strip away all the huff and puff, and all you're left with is a Horny Old Man.
(Incidentally, these stories are almost always written by Horny Old Men who think they are being terribly "intellectual". There are also examples, though much fewer, of "Horny Old Woman" plots.)
3. "Genocide Is Cool" plots:
Any plot which hinges on the hero killing off 100,000-1,000,000,000 (or more) "enemies". There is no way I'm going to admire such an atrocity, no matter what the excuse is.
(However, such plots have the potential for becoming award-winning, bestselling cult books, a fact which makes me very very depressed.)
4. "The Gadget Saves The Day" plots:
What John Boorman did right with the movie EXCALIBUR (and so many others fail at) is that when King Arthur pulls the sword out of the stone, this does NOT automatically remove all obstacles or make everybody obey him.
In the real world, entire empires and peoples will not suddenly become enslaved by a magic trinket. That's just impossible. (Except in some SF and fantasy.)
5. "Talk About Your Feelings" plots:
A plot in which no resolution or significant change occurs, except that the protagonist gets to Talk About Her Feelings. Very Nice and Humane and Kumbaya... and So Boring.
This may seem merely like an example of a "weak" plot (i.e. it lacks an underlying message and is only under-written), but I think it does carry a message.
Namely, that feelings are SO important that as long as the character has the "right" feelings, she can do whatever the heck she wants and not be responsible for it!
I'm sure you can come up with other examples of Plots You Hate.