This makes me think of the end of Evangelion (the anime, not the End of Evangelion film)...."This is the Shinji that you know on Facebook. This is the Shinji you know on Twitter. This is the Shinji you know in real life..." etc.

I kind of half-realized this in middle school; I noticed that I acted different in front of my friends and in front of my classmates, and my parents, and teachers. Then, when I went to college I realized I was different with my college friends than I was with my middle or high school friends. I think people mostly have herd tendencies, and I feel like most social groups (IRL at least) have a leader (or leaders) who set the tone for how the group will act.

One group of friends from when I worked at a bar were all loud and crazy, so when I hung out with them, I was loud and crazy.
At home, I'm boring and quiet.

I think humans are just like this. We are pack creatures, like it or not.
Some of us adjust to a solitary lifestyle, and we are adaptable, but in a group, I think most people would take on the role the "leader" has prescribed.

Sorry for tl;dr.