My female Fire Clown loves attacking me any chance she gets. Sometime just the force of the hit is enough to send me jumping in the air. Other times she is skilled enough to bite the soft skin in between the fingers.....that HURTS! Other times it is just an annoyance.
Regards intra-fish aggression, in my 14 gallon cube I have failed to keep any midsize/mid water column fish with the Fire Clown (Royal Gramma, Cryptic Wrasse, male Fire Clown), but the female has no interest whatsoever in the 9 tiny gobies I have in the tank, totally ignoring them: green banded gobies, red banded/high fin goby, yellow neon/cleaner hybrids, red striped, yellow clown, and red headed. I guess they are so small that it simply doesn't view them as a threat. Nor has it tried to eat them, which I'm sure it would be capable of doing.