Had one... He was cool for about the first 4 months. Shy for the first 3 weeks, friendly for a couple of months, then BAM!!! It's like this little thing got ahold of some bath salts!!! He was chasing fish 8 times his size around the tank. He had my triggers scared to come out of hiding, and literally went after anything moving for no reason at all. I thought it was just a faze, so I watched him for a little while. After a week, or so, of this behavior, he had to go. He had other fish that normally got along with eachother so nervous that they started attacking eachother. After I removed him, all other fish calmed down, and peace was restored...
I'd like to say I'm exaggerating, but, I'm not. I took his candy tail back to the LFS...