High school acquaintances are most likely to be unfriended first in Facebook, according to a University of Colorado Denver study. A friend of a friend, colleagues and common interest friend are the next set of people that are predicted to disappear from Facebook over time.

"The most common reason for unfriending someone from high school is that the person posted polarizing comments often about religion or politics," Christopher Sibona, a doctoral student in the Computer Science and Information Systems program at the Business School, said in a press release. "The other big reason for unfriending was frequent, uninteresting posts."

For the study, the researchers conducted two experiments with 1,077 participants to determine unfriending attitudes and the emotional responses from the victims.

The researchers found that high school friends become top targets because they might not hold strong political or religious beliefs during their teens. And over time, if they become vocal and develop firm beliefs, they tend to offend their friends who don't share their opinions through Facebook posts or updates. Sibona said that disagreements intensify quickly on social media.

Facebook users removed co-workers from their friend list due their behavior at their work place rather than their online posts.

In the second experiment, the researchers discovered emotions of being unfriended on Facebook. The most common reactions connected to the expulsion were: I was surprised; It bothered me; I was amused and I felt sad, among others.

The researchers found that Facebook users get negatively affected when their best friend unfriends them. Users were less likely to be annoyed about being unfriended if he/she discussed the disagreements with the person who erased the names from the list.

They also discovered that unfriending happens more commonly among those who were once close buddies than acquaintances.

"Despite the preponderance of weak ties throughout online social networks, these findings help to place unfriending within the greater context of relationship dissolution. If you have a lot of friends on Facebook, the cost of maintaining those friendships is pretty low," Sibona said. "So if you make a conscious effort to push a button to get rid of someone, that can hurt."

The findings were published in the 2014 47th Hawaii International Conference on System Sciences.