My old Melanopus clow used to go to town on my hands whenever I put them in the tank. It would back up to the very back of the tank and take a swimming start to get me sometimes. It got really bad when I added an anemone, then it really became a territorial thing.
I had a pair of Percula clownfish for awhile and they were very peaceful anytime I put my hands in the tank. Then the male died and the female became very aggressive. She would bite me or chase my hand away anytime I got within 2 feet of her or the anemone she hosted in.
-Chris
Try it with a Lionfish in your tank.... Everytime i put my hand in the tank now, he comes darting towards my hand, I try and be as brave as I can but I heard they hurt pretty bad lol. Most of the time i can swoosh him away but during feeding, he jumps out of the water to get whatever im feeding him lol. Scares the heck out of me sometimes....