After reading Samuel, I realize that David was no saint, although I knew he had a little tangle with a woman and her husband. But it appears more and more evident that you really have to look at the big picture with the old testament. This isn't theology, its poetry. It's the expressions of a man, a sinner, who did both good and bad but was still loved by God and still loved God. These aren't exclusive concepts and chapters like these I don't see as a recommendation on how to pray or act but more affirmation that even those God loved the most had emotions and thoughts that were difficult to control. That being said, I also appreciate the other explanations for this somewhat alarming tirade that were offered in previous comments.

If this is chronological then maybe David is just a grumpy old man here. But I guess we can't write it off that easy as the psalm is preserved and has been used in worship by the Israelites for hundreds of years. I also look back to my previous entry. I think this chapter is useful for instruction, without mimicking it.