I really don't think that it's separation anxiety, but I can't think of anything else to call it.
My four month old DD has decided, in just the past week, that she hates her paternal grandfather. Or is at least scared of him. When we saw him last Wednesday, February 27, she was fine; she was happy, cooing, everything she normally does. But on Sunday, when we went to DF's grandma's house (her great-grandmother), every time we tried to give her to him, she'd take one look and scream bloody murder. She did the same thing to his brothers, too (DF's uncles), but had no problem with her great-grandma or DF's aunts.
This Wednesday, the 6th, we again went to Grandpa's house, like we have for weeks, and she did the same thing, even when he didn't try to hold her. I had her on the floor and he got down to play with her and she started fussing. He has seen her at least once a week, most of the time twice, since she was born. We have no other males near by to see if she would it it with them; my family lives five hours from us. But she has no problem with DF's mother, who she sees almost everyday, and is, if anything, becoming even more of a Daddy's Girl than she has been.
Does anybody have any theories? She has a doctor appointment next week, and if this trend continues, I will ask about it, but is it anything to worry about, or is it just a phase that she's going through and will outgrow? She's been fussy in general all week, too, if that makes any difference.