The day I got georeferenced, shaded, 3d terrain working for a synthetic vision system, singlehanded, in bare OpenGL ES 2.0.
Friend of mine at work took my picture seconds after I got it working, you can see the crazed look in my eye.
https://www.flickr.com/photos/24025582@N03/4150935582/in/dat...
The worst day of my professional life was probably the day Derek Sivers canned me because, "I want to do your job myself."