In the old days, email lists had filters, so when your brother-in-law sent you the 50th forwarded list of lawyer jokes, you just sent them right into the trash. On Facebook, it is not so simple - okay, actually it is, there is a hide feature built right in so you never see some things. But people still unfriend someone, which can lead to drama.
With 500 million users worldwide, Facebook can be an anthropology and psychology tool too. We have learned that experts can single out narcissists by their Facebook pages and that, brain activity-wise, the line between psychopathy and narcissism is slight.
So using the wealth of users available all on a common platform, Christopher Sibona, a PhD student in the Computer Science and Information Systems program at University of Colorado Denver, set out to answer the question a lot of angst-ridden teenage girls want to know; "why did you take me off your Facebook friend list?"
The number one reason - a lot of trivial, unimportant posts was number one (like my blog, given this topic).
Number two reason - too much talk of religion and politics. People on the Internet seem to have lost sight of the same common-sense rules our parents instilled in us, including our parents.
Read Science Codex for the rest.