The friend is a frequent visitor here, and my wife's best friend. In the past couple of years, even when Sammy was being antisocial, her visits have caused Sammy to get friendlier with me, wanting to be "up", cooing, making nice sounds, and enjoying lots of skritches and other physical attention. To be honest, I don't think she believed how mean he'd become, as she always saw the sweet side of him.
Now, however, she sees it - he treats her just like us, and when he's not being violent towards everyone in the room, he ignores her visits completely.
She's actually had a similar problem with her a male Eclectus, who has become a more or less permanently caged bird, although it's been gradual over the past 5-6 years. In her case, I suspect that the bird might be angry that he's not an "only bird" (although he's always had amorous intentions toward the other females in the flock, so he doesn't hate them), and is jealous over the attention she gives her other birds. Whatever the reason, she's had to go to hospital several times because he's attacked her out of the blue, and he has a very large, powerful beak.
Some have mentioned perfume, etc. - my wife's allergic to most scented products, so we don't use or wear anything scented in the house (and visitors are asked not to do so, as well).
To be honest, we've scoured every aspect of our lives - schedules, furniture changes, Sammy's toys (we've gone back to solely the ones he has always liked best), his diet, his treats, the TV shows we watch, people who visit (we live out in the sticks, so visitors are fairly rare, and those who do visit are the same ones as we've always had), the clothes we wear, etc., and we can't find a solitary thing that's remotely changed since Sammy was a lovable bird. He's always had hormonal periods, where he's been testy for a week or two, but this has been going on for months, and getting worse every day.
Our routine hasn't changed at all. Identical schedule for, well, everything. All the other birds are healthy, happy, and social, as they've always been. They're all rescues, and they've all blossomed in our care. Even Sammy, for the first year or so - he was "daddy's bird", closely bonded to me. Now, even my wife (who Sammy's always hated) agrees that Sammy simply isn't bonded to me anymore.
I can't express how sad it makes me to have lost that bond. I miss my Sammy...