When I first got it, my betta pecked at a mole on my forearm while I was rearranging the plants. I quietly muttered "hey, cut that out" and I seriously wanted to brush/flick it away like a fly but thought otherwise. Eventually he figured out it wasn't food and swam way. Nowadays, he kinda stares at it when my arm is in there.
I got bitten by an arrowana once... Not hard, he was'nt trying to take off a finger, just latched on and squeezed a bit. What I get for taking him out of a tank... Our oscar has caught us by the fingers a few times during feeding. He's got more appetite than sense.
My maroon clown bites me every time I stick my hand in the tank. Scared the crap out of me the first time. I guess it's funny to him and anyone watching.. but I don't care for it. lol. My anemone grabs on really good when I get to close. Thats always an odd sensation.
I have been bitten plenty of times by convicts and heard they can break skin but it hasnt happened yet. thats nothing thought compared to larger cichlids