The occurrence of someone being more attractive on their Facebook profile (or profile of any social networking site) than they are in real life. This is a reference to the fact that the actors in the 2010 film "The Social Network" were deceivingly more attractive than the people they were portraying, i.e. Armie Hammer vs. The Winklevoss Twins.
1: How'd your date go last night?
2: Not to well. I was really excited until I found out he was just Social Network Hot, then I was just depressed.
2: Remember when you saw Armie Hammer play the Winklevi?
2: And how hot, smart, and tall you though he was. And how much you liked him...
1: Oh yeah!
2: Then remember how you felt when you googled the actual Winklevi and saw what they really looked/sounded like?