Another example is a friend's husband. I just know the only reason he has friended me is to keep an eye out on his wife (he is the similar type as above just add abusive and mysogonistic to the list). I have unfriended him too and it gets back to me. He obviously expresses his displeasure to his wife and has forbidden her to contact me unless I keep him as a friend.

These are pretty extreme examples. I have wondered if others experience the same to any degree.