I get bitten by something every day, i am used to it now and it doesn't bother me. I would say that out of all the fish in the store it is the cichlids that make me jump the most. i have even had some of them draw blood, but it is all in a days work.
There was one fish that worried me once and that was a 36" Red Tail Cat fish that a friend of mine had. I went round to clean his tank for him, and while i was cleaning the aquarium glass the cat fish came up to me and took the Algae magnet and my hand. it took me a couple of seconds to realise that my hand was still connected to the algae magnet and he had taken it all, up to my wrist. But luckly enought he didn't like the taste of the algae magnet and let it go. And once i was helping a friend out in his store and i was cleaning out this tank, i didn't get bitten but i got thrown across the store when i got a shock from the Electric Catfish that lived in the tank, i thought the tank was empty. (how wrong was i) My friend thought it was really funny, and was laughing for a week.