When the vote dump from the FL panhandle came in with several hundred thousand Trump votes. In a split second it went from "we got this, and I can go to bed early," to "Oh, crap."
Basically this, around 1:30 am my time. I was getting increasingly concerned about how well Trump was holding up in Miami-Dade and Broward, then the flood of votes from the Panhandle came in and I started to panic. Then the Michigan exit poll came out showing the state tied and I knew Trump had won.
It is interesting how few people were expecting it. I don't believe it, but I would have assumed that most people would have had at least the "maybe just maybe" feeling well before November 8. My friend was that way. He thought Hillary would win, but stated he felt like there was about a 25 percent chance Trump would win
For my part it had a lot to do with how 2012 had turned out. After the first debate Obama had a small but consistent lead over Romney and I was annoyed with the media for portraying the race as closer than it actually was, along with tons of Republicans spinning unskewed polls, then the polling error was in Obama's favour. I sort of assumed the same thing would happen again.