I have only owned Colombian RBs. My first was a wild caught adult, which was extremely defensive. Captive raised babies were pretty mellow. So IMO, the nippy reputation may be a holdover from the times when almost all captive RBs were wild caught adults. There are a number of species that have bad reputations for that reason (eastern diamondback rattlesnake, pine/bull/gopher snakes, North American water snakes, etc.).

For what it's worth, a friend of mine has bred BRBs. His adult snakes are puppy dog tame.