4. Theon Feels Up His Sister
The Moment: Theon had been happily in the background for much of Thrones first season, filling the role of just another Stark ally, but he brought a dependency that made his turn against those who can technically be called his captors still shocking. Thats not to say it was a total surprise. In the episodes leading up to his taking of Winterfell, we began to see a seedier side of him; sleeping with slutty ship captain's daughter and, in a moment sickening only when you discover the truth afterwards, feeling up his sister.
Why It's So Sickening: Incest really shouldn't be too much of a shock in Game Of Thrones given that its first episode ended with some royally shocking twin action, but this moment tops that in the disgusting stakes because of how the participants react Theon is naturally distraught, but Yara seems to have been happy messing with her brother. As its played less morally ambiguous than Jaime and Cersei (at the time we learnt of their relationship the Lannisters seemed to be filling the stereotypical bad guy role) it has more resonance that the much more graphic Joffrey-makers.