I find watching/experiencing the subtle "dance" we call "interpersonal interactions" quite fascinating; the subtle changes in roles from a one-on-one with a loved one to a end-of-school or a get-to-know-your-coworkers picnic to a corporate board meeting or a doctoral dissertation defense.
I have found certain subtleties show up on different "stages". Take for instance, you are alone with your SO at home. Would you interact with her the same way you would the CEO of the company you work for?
One of my professors interacts with me differently when he's teaching the class than when we're both "students" or when we're discussing something over a cup of tea/coffee/whatever or when discussing anime/manga vs Russian/Ukrainian cartoons/"comic books". I interact differently with the people I RP with than with the neighbors I'm on speaking terms with or the people at the store/farmers markets (and we won't discuss interacting with furred purrsons [aka :kitty:s].)
I just like learning about the puzzle we call "society" (or is it "human interaction"? *shrug*) If I can remember better examples, I'll post them later.
Phyllis Sidhe_Uaine