It happens to me ALL THE FREAKING TIME. Take Giggles epic moment turned to poo, trust me, the moment when Giggles finds out that she's been deserted looked a hell of a lot better in my head than what finally got turned out in print (although I will admit I think I did okay with the hiding sequence). When Joe died was supposed to be a bit more epic too (helicopter chases and everything, although I had to scrap most of it because it was SO out-of-character and wouldn't have made any sense in the context of the C&G world). About the only things I feel I got right were the reformation of Chuckles and Giggles and the rather lacklustre first date between 24-42 and M42 (I had SO much fun writing that, as much as I hate writing love stories. I'm sure everyone has a wonderful first awkward first date story).
It doesn't matter how long you spend on some of these pieces (it took me a month to get the beginning of chapter 41 of Chuckles and Giggles done, and even after that I'm not 100% thrilled by it), you simply never feel like you've done the scene in your head justice.
Of course, then there's the fun task of explaining how characters got from point A to point B. Neither of my stories would be any chop if I just went "These two became friends, then their school got invaded so years later they became superheroes with some other kids and then they became friends with the school bully." Writing in "filler" is a complete and utter drag in my honest opinion, and the biggest cause of writers block for me. Thankfully I've managed to combat this somewhat with a more episodic approach to my chapters, but I can't wipe out the need for it altogether.
The worst of all is when I know I've been neglecting this blog (which I do regularly...I'm sorry!) and I'm racking my brains for ideas when I know I had one twenty minutes ago on the train and I was too zoned out in my own imagination to think of writing it down (I'm bad, I know). I'd appeal for suggestions, but that would draw the ever-wonderful "You should write about what you want to write about" suggestion and I don't have enough room in my yard to bury that many bodies.
Maybe I should find a random subject generator, there's bound to be one somewhere on Google...
This is my Gyarados picking on a Magikarp. He's awesome like that.