Burbs.. sigh. My green cheek, Batburd, would frequently walk on the top of their cage upside down. More so than other birds i've owned, which got them their name, LOL.
Sunny occasionally hangs upside down and often sleeps in that position.
John... humps the swing. It's really awkward. Most of the time he can control himself, but sometimes he doesn't. He's also mated with snowy, luckily I got zero babies.
My budgie Gertjie(may she rest in peace) loved climbing in your hair and chewing it.