Oh yeah... they can be nasty... My african grey... curently is not a problem... Very Friendly... but that might change when he grows up and breeding season kicks in about 5 years from now.
My Blue and Gold is out for Blood.... 48 hours after I moved him and his mate into a new cage... and he still wants to kill me... If he sees me and cant get to me, he attacks the female... if he does not see me... he's fine and leaves her alone. I did not want to take the chance so I had to move him out of his new cage and put him back in the "Introduction cage". His female stayed in there new cage... shes doing fine.. Very friendly... poor thing... its so sad that her boyfriend is abusive.
the blue and gold will stay in the "Introduction cage" for a few weeks... until he calms down... Im getting 2 new blue and gold males in 2 weeks... so I might just use one of those males with my blue and gold female... Figure give her a better husband than some jerk.