Dissertation Deadline. After working pretty hard over the summer (more so in the few days before this), and finishing it at about 2:00 the night before, I managed to hand my dissertation in just three minutes before the 12:00 deadline. Good timing!
I also had to give a presentation the next day which, despite Virginie Ruiz's (mostly) incorrect corrections, didn't go too badly. Ignoring technical glitches.
Basically I was just very happy to have this over with, so didn't care much how well or badly it went - this was the last thing I would have to do for the MSc, so it felt good to have a year of hardcore work officially behind me.