Blue screen that you're all too familiar with if you use an older version of windows. If you can't wait the ten minutes it takes to crash, just put a floppy disk or cd in and then take it out while trying to load something from it.
Last year at my school there was a slideshow with pictures of the seniors at an assembly. I laughed my ass off when the blue screen of death showed up halfway through their shitty powerpoint presentation.
That 30 minutes or so just before sunrise when everything in the world has a blue tinge to it. Usually noted to point out the fact that you've been up all night.
"How late did you guys stay up last night?"
"Oh, it was bluetime when everyone went home."