Writing Good Dialogue

There's nothing more frustrating to me than writing good dialogue, and for good reason. While overall quality of one's writing is essential to producing something worth reading, it's the dialogue that really defines one's characters and gives them the essence of being alive rather than some kind of 2d caricatures. Take these examples if you will:

An Example of Good Dialogue:

"Damn it."
"What?"
"I forgot my phone back in the office yesterday."
"Wait! What? Are you stupid? We just stole the answers to the fucking final!"
"I know, I know! We've gotta get it back!"
"We? Ha! You, my friend, are the one who needs to get your phone back! It's not me they're going to expel from the university if they find out."
"Oh, so you're just going to abandon me! What kind of friend are you?"
"A smart one, amigo, a smart one. I've already invested over 50k for that little slip of paper that says you're no longer just any burger flipper, you're a burger flipper with credentials. There's no way I losing out on that."
"You know, when you put it that way, stealing the answers was totally worth it."

(If this actually an example of good dialogue, then it's a fluke for me)

And an Example of Bad Dialogue (Taken from the Twilight Series, by Stephenie Myer):

"And for all that," he continued, "I'd have fared better if I /had/ exposed us all at that first moment, than if now, here--with no witnesses and nothing to stop me--I were to hurt you."

I was human enough to have to ask. "Why?"

"Isabella." He pronounced my full name carefully, then playfully ruffled my hair with his free hand. A shock ran through my body at his casual touch. "Bella, I couldn't live with myself if I ever hurt you. You don't know how it's tortured me." He looked down, ashamed again. "The thought of you, still, white, cold . . . to never see you blush scarlet again, to never see that flash of intuition in your eyes when you see through my pretenses . . . it would be unendurable." He lifted his glorious agonized eyes to mine. "You are the most important thing to me now. The most important thing to me ever."

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So, as you can see, there's a BIG difference between dialogue that actually brings the characters to life, and dialogue that makes the characters predictable, flat, and ultimately uninteresting. And this is where my problems come in; I cannot, for whatever the reason, write dialogue that I'm actually satisfied with. Perhaps I'm too critical of myself, or perhaps my talent for writing is restricted to my ability use proper grammar and syntax.

And this really gets to be the problem when you've started a story 3 times, each averaging about 4 or 5 pages, before you start to realize that you hate how your characters are interacting.

Fuck it. I need a drink.