Its all up to the individual personality of the fish, how its raised, the conditions its raised in, the size tank its kept in, how comfortable it is... the list goes on.
I used to have 4 Red Bellies In a 40 Breeder tank. They used to kill everything that i put in there from crabs to plecos. One time while i wasnt home my uncle put in a kissing gourami like triple there size they killed it and ate it. After that i havent had any pirahnas since. So i woudnt know