*screaming sound*

i didn't touched one on the butthole, but we have 2 of this birds (same species) @ home and.. well, let's say they can be really rude :D

So one of your bird is into anal and the other isn't

Nah

Can confirm, parrots can be really vicious. Usually they have a good reason for biting, though, unless they were socialized very poorly. A little Tiel like that isn't going to hurt much, but my Grey, for instance, could take half my finger off, even though she's mostly very sweet. Which is why I've never tried to boop her butt.