Nielson Media has finally answered one of the pressing mysteries of the age: Why we defriend people on Facebook. Surprisingly, the top reason isn’t overusing played-out memes. The most likely answer: because someone offended us. That data comes courtesy of a study of 1,865 adult users of social media, conducted from March 31st to April 14th. It found that as in real life, behaviors like having creepy friends, insisting on saying terrible things, or simply being a depressing downer play a huge role in choosing with whom we socialize.

By a wide margin, the top reason for removing someone as a friend, cited by 55% of respondents, was “offensive comments”. What, precisely, is meant by “offensive” is unexplained; “political comments” (14%) are considered a distinct reason apart from generally offensive comments. This suggests that the offenses referred to are more personal in nature, unsurprising to anyone fortunate enough to witness a very embarrassing argument conducted for all to see on a Facebook user’s wall.

Not knowing someone well was the second most common reason for de-friending someone, cited by 41% of respondents, and “trying to sell me something” came in at a very close third place, with 39%. Other reasons include “depressing comments” (23%), “lack of interaction” (20%) Breakups and divorce (11%). “Update profile too often” and “they added too many people” are tied with 6% of respondents citing them, a lesson to anyone who thinks that the rest of us are as enthralled by constant declarations of true love, or their children’s latest potty training update as they are.

In addition to de-friending habits, the study also shows that men and women use social media in subtly different ways. Both men and women primarily use such services to keep in touch with family, reconnect with old friends and find new ones. However, men showed a higher likelihood of using social media for professional networking and dating, with a corresponding tendency to approve friend requests if the requesting user is attractive. Women on the other hand had a higher tendency to cite creative expression and positive reinforcement as primary reasons for using social media. Interestingly, the data suggests much higher commonalities among women. The top reasons for approving friend requests or for removing someone as a friend were cited more by women than by men.

The only thing missing from Nielsen Media’s research is a comprehensive examination of people who decide they’ve had enough of Facebook and ostentatiously announce that fact via an angry post to their Facebook wall that contains phrases like “LOL I hate Fakebook!” and “I’m getting back to real life!”. This is most likely due to the fact that such people have also been defriended in real life.

The report can be read in full on the official site.