One reason he believes high school friends are top targets for unfriending is that their political and religious beliefs may not have been as strong when they were younger.
And if those beliefs have grown more strident over time, it becomes easier to offend others.
"Your high school friends may not know your current political or religious beliefs and you may be quite vocal about them," Sibona said.
"And one thing about social media is that online disagreements escalate much more quickly," Sibona said.
The second study looked at the emotional impact of being unfriended.
Sibona found a range of emotions connected to unfriending, from being bothered to being amused.
The most common responses to being unfriended were: 'I was surprised', 'It bothered me', 'I was amused' and 'I felt sad'.
"The strongest predictor is how close you were at the peak of your friendship when the unfriending happened," said Sibona.
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