I had three yellow tail damsel. One got picked on so bad by the other two I took it back to the LFS. I do think they are a little mean. My fish have been together in my tank since I set it up a year ago and everything seems peaceful. I'd like to get rid of a couple of chromis and add a hippo tang, but I am afraid of what my damsel's might do to it. Adding fish is always scary to me. I lost a newly introduced yellow tang from a clown fish beating her one time.
I currently have 2 yellowtail damsels, 1 yellow tang, 1 clown fish, and 4 Blue/Green Reef Chromis (had 5 but one died recently) in my 75 gal tank. They all seem pretty happy.