I dunno, Pinkie Pie's flaw is pretty clear to me.
She does not communicate well. She either overcommunicates or doesn't communicate at all.
Not to mention that taking things seriously is hard for her, to the point where even when she goes into "srs mode", she's still taking things humorously. Look how she acts during the Parasprite invasion. She makes a non-sequiter (which is LATER proven to be otherwise) and leaves. What is she like when she's not serious? Non-sequiter.
And the dance. She failed that dance horribly. And even after it failed, she tried the exact. same. thing. One definition of insanity is "Trying the same thing over and over again and expecting different results."
So yes, she's clearly insane. I would imagine it has something to do with her leading a mind-numbingly boring life and then receiving a brain shock upon seeing the shockwave of the Sonic Rainboom. It's like going from a room that's freezing cold into a room that's blazing hot. You'll injure yourself doing that.
To be honest, the only Sue we really have is Celestia, and even that's justified due to her being dangerously genre savvy, as well as a freaking deity. And even then, she's a prankster troll herself, so even her Sue-ish traits are done well.
So, long story short, Lauren Faust is dangerously genre savvy herself, knows how to avoid a sue, and when to make a Sue so that she can desconstruct her.
edited 18th Apr '11 9:24:38 PM by Zachski